We present the results and the lessons learned from two separate and independent studies into the design, development, and evaluation of electronic books for information access: the Visual Book and the Hyper-TextBook. The Visual Book explored the importance of the visual component of the book metaphor in the production of "good" electronic books for referencing. The Hyper-TextBook concentrated on the importance of models and techniques for the automatic production of functional electronic versions of textbooks. Both studies started from similar considerations on what kinds of paper books are suitable for translation into electronic form but di.er on the prominence given to book appearance and functionalities. The results of these two research projects are critically presented in this paper, with the aim of helping designers and implementers to better integrate appearance and functional aspects of books into a more general methodology for the automatic production of electronic books for information access.

We present the Lorel language, designed for querying semistructured data. Semistructured data is becoming more and more prevalent, e.g., in structured documents such as HTML and when performing simple integration of data from multiple sources. Traditional data models and query languages are inappropriate, since semistructured data often is irregular: some data is missing, similar concepts are represented using different types, heterogeneous sets are present, or object structure is not fully known. Lorel is a user-friendly language in the SQL/OQL style for querying such data effectively. For wide applicability, the simple object model underlying Lorel can be viewed as an extension of the ODMG data model and the Lorel language as an extension of OQL. The main novelties of the Lorel language are: (i) the extensive use of coercion to relieve the user from the strict typing of OQL, which is inappropriate for semistructured data; and (ii) powerful path expressions, which permit a flexible form of declarative navigational access and are particularly suitable when the details of the structure are not known to the user. Lorel also includes a declarative update language. Lorel is implemented as the query language of the Lore prototype database management system at Stanford. Information about Lore can be found at http://www-db.stanford.edu/lore. In addition to presenting the Lorel language in full, this paper briefly describes the Lore system and query processor. We also briefly discuss a second implementation of Lorel on top of a conventional object-oriented database management system, the O2 system.

The World Wide Web is a large, heterogeneous, distributed collection of documents connected by hypertext links. The most common technology currently used for searching the Web depends on sending information retrieval requests to "index servers" that index as many documents as they can find by navigating the network. One problem with this is that users must be aware of the various index servers (over a dozen of them are currently deployed on the Web), of their strengths and weaknesses, and of the peculiarities of their query interfaces. A more serious problem is that these queries cannot exploit the structure and topology of the document network. In this paper we propose a query language, WebSQL, that takes advantage of multiple index servers without requiring users to know about them, and that integrates textual retrieval with structure and topology-based queries. We give a formal semantics for WebSQL using a calculus based on a novel "virtual graph" model of a document network. We propose a new theory of query cost based on the idea of "query locality," that is, how much of the network must be visited to answer a particular query. We give an algorithm for characterizing WebSQL queries with respect to query locality. Finally, we describe a prototype implementation of WebSQL written in Java.

The Standard Generalized Markup Language (SGML) and the Extensible Markup Language (XML) allow users to define document-type definitions (DTDs), which are essentially extended context-free grammars expressed in a notation that is similar to extended Backus-Naur form. The right-hand side of a production, called a content model, is both an extended and a restricted regular expression. The semantics of content models for SGML DTDs can be modified by exceptions (XML does not allow exceptions). Inclusion exceptions allow named elements to appear anywhere within the content of a content model, and exclusion exceptions preclude named elements from appearing in the content of a content model. We give precise definitions of the semantics of exceptions, and prove that they do not increase the expressive power of SGML DTDs when we restrict DTDs according to accepted SGML practice. We prove the following results: 1. Exceptions do not increase the expressive power of extended context-free grammars. 2. For each DTD with exceptions, we can obtain a structurally equivalent extended context-free grammar. 3. For each DTD with exceptions, we can construct a structurally equivalent DTD when we restrict the DTD to adhere to accepted SGML practice. 4. Exceptions are a powerful shorthand notation — eliminating them may cause exponential growth in the size of an extended context-free grammar or of a DTD.

This paper describes a number of ways to encode spatiotemporal information in RSS feeds. As RSS becomes more and more prevalent as a way to publish and share information, it becomes increasingly important that location and time is described in an interoperable manner so that applications can request, aggregate, share and map spatiotemporally tagged feeds. This paper describes the GeoRSS model and encodings. With every RSS item has a timestamp, GeoRSS can represent time property for free. There are three GeoRSS encoding standards, such as W3C Geo, GeoRSS Simple, and GeoRSS GML profile. These standards differ in the number of coordinate systems they can support, and in the number of different geometric shapes they can add to the map to show where the news or event of interest is taking place. Further more, this paper described how to add time attribute to GeoRSS and implement and visualization the GeoRSS feeds through Google Map and Timeline. A few apt illustrations were given to show the powerful functions of GeoRSS in syndicating the spatiotemporal information. GeoRSS leverages this teeming ecosystem for geospatial technology, and with OGC support, GeoRSS is on firm conceptual ground and gains exposure across the industry.

In this paper, we investigate the problems associated with the provision of an undo support facility in the context of a synchronous shared or group editor. Previous work on the development of formal models of undo has been restricted to single user systems and has focused on the functionality of undo, as opposed to discussing the support that users require from any error recovery facility. Motivated by new issues that arise in the context of computer supported cooperative work, we aim to integrate formal modelling of undo with an analysis of how users understand undo facilities. Together, these combined perspectives of the system and user lead to concrete design advice for implementing an undo facility. The special issues that arise in the context of shared undo also shed light on the emphasis that should be placed on even single user undo. In particular, we come to regard undo not as a system command to be implemented, but as a user intention to be supported by the system.

Knowledge regarding how Web information-seekers behave with respect to the structures and cues they are provided with may shed light on general principles of navigation in electronic spaces, and assist designers in making more informed structural decisions. This study examines user movement through hierarchically structured Web sites and the behavioral effects of a constantly visible, textual contents list for relatively small sites or more extensive local views than are generally used on the Web today. The site overview resulted in users abandoning fewer information-seeking tasks. Users with such context dig deeper into the site structure, make less use of the browser's Back button, and frequently make navigational movements of great hierarchical distances. Navigational correlates of success and reported confidence for users with the overview differ from those without such context. Both with and without a constant overview, the relationship between the source and destination pages may help predict the amount of time spent at the destination. Experimental reports are preceded by a review of click-stream navigation behavior research.

Purpose: A growing amount of information available on the Web can be classified as "contextual information", putting already existing information into a new context rather than creating isolated new information resources. Blogs are a typical and popular example of this category. By looking at blogs from a more context-oriented view, it is possible to deconstruct them into structures which are more contextual than just focused on the content, facilitating flexible reuse of these structures. — Design/Methodology/Approach: We look at the underlying structures of blogs and blog posts, representing them as multi-ended links. This alternative representation of blogs and blog posts allows us to represent them as reusable information structures. This paper presents blogs as a popular content type, but the approach of restructuring Web 2.0 content can be extended to other classes of information, as long as they can be regarded as being mainly contextual. — Findings: By deconstructing blogs and blog posts into their essential properties, we can show how there is a simple and universal representation for blogs. This representation allows the reuse of blog information across specific blog or blogging platforms, and can even go beyond blogs by representing other Web content which provides context. — Originality/Value: The approach presented in this paper is a novel approach of mapping a popular Web content type to a simple and universal representation. The value of such a unified representation lies in exposing the structural similarities among blogs and blog posts, and making them available for reuse.

This paper traces the development of World Wide Web Robots and provides an overview of their main functions and workings. The focus is on search robots and illustrations will be drawn from two major search engines: AltaVista and Excite. In the concluding section, problems associated with the use of Web Robots and their implications for electronic publishing will be examined.

NameSet is a system that translates a set of geographic coordinates into a textual name based on the geographic regions where the coordinates occur. One possible application of NameSet is to concisely present the geographical scope of a set of geo-referenced observations to a human user. Another application is to generate text to depict a set of coordinates that appear on a web site — text that could later be used for information retrieval applications. NameSet's computation is based on a simple algorithm, using off-the-shelf and web-based data sources. The system was proven effective in an application that automatically organizes and names sets of geo-referenced digital photographs.

In today's highly competitive wireless marketplace, carriers have to offer user-friendly, innovative services to gain a competitive advantage. Furthermore, subscribers demand services that can be easily customized to their specific needs. The advent of the wireless application protocol (WAP) and WAP-enabled mobile phones is providing an opportunity for carriers to leverage this technology to enrich their service offerings. WAP is becoming the de facto standard for mobile subscribers who want to browse the contents in the Internet and perform e-commerce transactions. At the same time, new capabilities — such as those provided by intelligent network (IN) technology — are also being introduced into the public land mobile networks (PLMNs) to provide enhanced services. This paper discusses how the emerging WAP technology can be synergistically combined with PLMN capabilities to provide mobile subscribers with enhanced converged voice/data services in WAP-enabled wireless networks. To illustrate these concepts, this paper includes several service examples.

This paper traces the history of location-based service (LBS) standards that arose from North American requirements in the work on GSM standards in the late 1990s. It also describes how interest in GSM/UMTS outside Europe led to the creation of the Third Generation Partnership Project (3GPP) for developing UMTS standards (which include standards for the 3G mobile Internet). In addition, the paper covers the role of other standards bodies and interest groups involved in the creation of LBS standards such as the new Open Mobile Alliance. Different location methods for detecting the position of mobiles are described and a summary of the current work in 3GPP on LBS-based services and architecture for UMTS is given. The paper also covers work on wireless access protocols in the old WAP Forum on LBS and also the work of the Location Interoperability Forum (LIF). Finally, the impact of these LBS standards developments on BTexact initiatives, such as project Erica, is summarised. The provision of a rich range of LBS services is considered to be very important for the future success of UMTS.

This paper provides an overview of terms, technologies and standards used within the location-based services field in the determination and presentation of the location of an entity. A description is provided of data formats and protocols for communicating, storing and manipulating location information and some insight is given into how location information could be used in a range of applications.

Purpose — Aims to describe systematically the characteristics of weblogs (blogs) — frequently modified web pages in which dated entries are listed in reverse chronological sequence and which are the latest genre of internet communication to attain widespread popularity. Design/methodology/approach — This paper presents the results of a quantitative content analysis of 203 randomly selected blogs, comparing the empirically observable features of the corpus with popular claims about the nature of blogs, and finding them to differ in a number of respects. Findings — Notably, blog authors, journalists and scholars alike exaggerate the extent to which blogs are interlinked, interactive, and oriented towards external events, and underestimate the importance of blogs as individualistic, intimate forms of self-expression. Originality/value — Based on the profile generated by the empirical analysis, considers the likely antecedents of the blog genre, situates it with respect to the dominant forms of digital communication on the internet today, and suggests possible developments of the use of blogs over time in response to changes in user behavior, technology, and the broader ecology of internet genres.

The purpose of this article is twofold. First, we summarize research on the topic of privacy in Human-Computer Interaction (HCI), outlining current approaches, results, and trends. Practitioners and researchers can draw upon this review when working on topics related to privacy in the context of HCI and CSCW. The second purpose is that of charting future research trends and of pointing out areas of research that are timely but lagging. This work is based on a comprehensive analysis of published academic and industrial literature spanning three decades, and on the experience of both ourselves and of many of our colleagues.

The Back button on web browsers is one of the world's most heavily used user interface components, yet its behaviour is commonly misunderstood. This paper describes the evaluation of a "temporal" alternative to the normal "stack-based" behaviour of Back and Forward. The main difference of the temporal scheme is that it maintains a complete list of previously visited pages. The evaluation compares the efficiency of the stack and temporal schemes in an "out of the box" scenario in which participants were asked to use a "new" version of a commercial browser without any explanation of the presence or absence of new features. This scenario allows us to predict the likely usability impact if commercial browsers were released supporting the temporal scheme. The results showed that the relative efficiency of the two schemes differed across different types of navigational task. In particular, the temporal system poorly supported backtracking to parent pages, but performed better for more distant navigation tasks. The temporal scheme also caused extreme usage patterns, with the subjects either solving tasks very efficiently or very inefficiently, depending on whether they used the Back menu. This observation indicates that adaptations of the temporal system that improve the effectiveness of the Back menu may enhance web navigation.

There is a new wave of business communication tools including blogs, wikis and group messaging software — which the author has dubbed, collectively, Enterprise 2.0 — that allow for more spontaneous, knowledge-based collaboration. These new tools, the author contends, may well supplant other communication and knowledge management systems with their superior ability to capture tacit knowledge, best practices and relevant experiences from throughout a company and make them readily available to more users. This article offers a paradigm that highlights the salient characteristics of these new technologies, which the author refers to as SLATES (search, links, authoring, tags, extensions, signals). The resulting organizational communication patterns can lead to highly productive and highly collaborative environments by making both the practices of knowledge work and its outputs more visible. Drawing on case studies and survey data, the article offers managers a set of ground rules for implementing the new technologies. First, it is necessary to create a receptive culture in order to prepare the way for new practices. Second, a common platform must be created to allow for a collaboration infrastructure. Third, an informal rollout of the technologies may be preferred to a more formal procedural change. And fourth, managerial support and leadership is crucial. Even when implanted and implemented well, these new technologies will certainly bring with them new challenges. These tools may well reduce management's ability to exert unilateral control and to express some level of negativity. Whether a company's leaders really want this to happen and will be able to resist the temptation to silence dissent is an open question. Leaders will have to play a delicate role if they want Enterprise 2.0 technologies to succeed.

Drawing upon a wealth of data, informed experience, and expert opinion — from Thomas Friedman to Bjarne Stroustrup, from David Gelernter to Nicholas Carr — the author builds a case that enterprise software in large organizations has not delivered on its promise to fully integrate and intelligently control complex business processes while remaining flexible enough to adapt to changing business needs. Instead, ERP systems — including both software applications and the data they process — are variegated patchworks, containing 50 or more databases and hundreds of separate software programs installed over decades and interconnected by idiosyncratic, Byzantine, and poorly documented customized processes. To manage this growing complexity, IT departments have grown substantially: Today's IT departments spend 70% to 80% of their budgets just trying to keep existing systems running. The research shows, says the author, that the typical IT structure is so dense and extensive that it's often a miracle that it works at all. Enterprise systems that were supposed to streamline and simplify business processes instead have brought high risks, uncertainty, and a deeply worrying level of complexity. Rather than agility, they have produced rigidity and unexpected barriers to change, a veritable glut of information containing myriad hidden errors, and a cloud of questions regarding their overall benefits. How did this happen? Rettig points to the inherent limitations in the nature of software, the costs of implementation, and the vagaries of data. Indeed, she offers, enterprise software may be just too complex to deliver on its promises. She also suggests that the next new thing — service-oriented architecture (SOA) — is not likely to fare much better, for many of the same reasons. There are no easy fixes, cautions Rettig, save a large dose of sobriety, clear-eyed analysis, and emphasis on simplicity and efficiency.

In contrast to the prevailing image that elements in organizations are coupled through dense, tight linkages, it is proposed that elements are often tied together frequently and loosely. Using educational organizations as a case in point, it is argued that the concept of loose coupling incorporates a surprising number of disparate observations about organizations, suggests novel functions, creates stubborn problems for methodologists, and generates intriguing questions for scholars. Sample studies of loose coupling are suggested and research priorities are posed to foster cumulative work with this concept.

Diverse applications of the concept of loose coupling are embodied in five recurring voices that focus separately on causation, typology, effects, compensations, and outcomes. Each has a tendency to drift away from a dialectical interpretation of loose coupling toward a unidimensional interpretation of loose coupling, thereby weakening the explanatory value of the concept. The authors first use the five voices to review the loose coupling literature and then to suggest more precise and more productive uses of the concept.

Social network sites (SNSs) are increasingly attracting the attention of academic and industry researchers intrigued by their affordances and reach. This special theme section of the Journal of Computer-Mediated Communication brings together scholarship on these emergent phenomena. In this introductory article, we describe features of SNSs and propose a comprehensive definition. We then present one perspective on the history of such sites, discussing key changes and developments. After briefly summarizing existing scholarship concerning SNSs, we discuss the articles in this special section and conclude with considerations for future research.

iPhone hackers, spectrum auctions, new carrier technology might doom mobile network carriers' "garden wall" restrictions on consumer choices.

Governments around the world are considering implementing or even mandating open standards policies. They believe these policies will provide economic, socio?political, and technical benefits. In this article, we analyze the failure of the Massachusetts's open standards policy as applied to document formats. We argue it failed due to the lack of running code. Running code refers to multiple independent, interoperable implementations of an open standard. With running code, users have choice in their adoption of a software product and consequently economic and technological benefits. We urge governments to incorporate a "running code" requirement when adopting an open standards policy.

Scholars, advertisers and political activists see massive online social networks as a representation of social interactions that can be used to study the propagation of ideas, social bond dynamics and viral marketing, among others. But the linked structures of social networks do not reveal actual interactions among people. Scarcity of attention and the daily rhythms of life and work makes people default to interacting with those few that matter and that reciprocate their attention. A study of social interactions within Twitter reveals that the driver of usage is a sparse and hidden network of connections underlying the "declared" set of friends and followers.

People often implicitly ascribe the quality of peer-production projects such as Project Gutenberg or Wikipedia to what I call "laws" of quality. These are drawn from Open Source software development and it is not clear how applicable they are outside the realm of software. I look at examples from peer production projects to ask whether faith in these laws does not so much guarantee quality as hide the need for improvement.

While browsing the Web is a widespread everyday activity there is a shortage of detailed understanding of how users organise their Web usage. In this paper we present results from a qualitative in-depth interview study of how users browse the Web and combine browsing with their other activities. The data are used to explore three particular problems which users have with browsing the Web. Firstly, users have problems managing their favourites, and in particular accessing their favourites through a hierarchical menu. Second, users have problems with combining information across different Web sites — what we call the "meta-task" problem. Third, users have concerns with security and privacy, although these concerns seem to change as users become more experienced with shopping on the Web. We discuss three concepts which address these problems: "home page favourites", "Web clipping" and the "Web card". These concepts are attempts at incremental improvements to the Web without affecting the Web's essential simplicity.

This paper describes the MARCXML architecture implemented at the Library of Congress. It gives an overview of the component pieces of the architecture, including the MARCXML schema and the MARCXML toolkit, while giving a brief tutorial on their use. Several different applications of the architecture and tools are discussed to illustrate the features of the toolkit being developed thus far. Nearly any metadata format can take advantage of the features of the toolkit, and the process of the toolkit enabling a new format is discussed. Finally, this paper intends to foster new ideas with regards to the transformation of descriptive metadata, especially using XML tools. In this paper the following conventions will be used: MARC21 will refer to MARC 21 records in the ISO 2709 record structure used today; MARCXML will refer to MARC 21 records in an XML structure.

Internet historians recognize the technical achievements but often overlook the bureaucratic innovations of Internet pioneers. The phrase, "We reject: kings, presidents, and voting. We believe in: rough consensus and running code," was coined by David Clark in 1992. This article explains how the phrase captured the technical and political values of Internet engineers during a crucial phase in the Internet's growth.

Conceptual modelling is situated in the broader view of information systems requirements engineering. Requirements Engineering (RE) explores the objectives of different stakeholders and the activities carried out by them to meet these objectives in order to derive purposeful system requirements and therefore lead to better quality systems, i.e., systems that meet the requirements of their users. Thus RE product models use concepts for modelling these instead of concepts like data, process, events, etc., used in conceptual models. Since the former are more stable than the latter, requirements engineering manages change better. The paper gives the rationale for extending traditional conceptual models and introduces some RE product models. Furthermore, in contrast to conceptual modelling, requirements engineering lays great stress on the engineering process employed. The paper introduces some RE process models and considers their effect on tool support.

Internet scamming strategies associated with West Africa typically involve the creation and deployment of fictional narratives depicting political turmoil, corruption, violence, poverty, and personal tragedy set in a variety of African nations. This article examines Internet scammers complicity in promoting these creatively dramatic and yet stereotyped representations of Africa and Africans. Their approach is an example of what De Certeau describes as a 'tactic' where scammers manipulate the space of representations produced by hegemonic forces in the West to realize subversive ends. The attempts of Internet scammers highlight the difficulties of creating selfrepresentations that are both 'authentic' and persuasive underlining the complexity inherent in efforts by marginalized communities to be heard by those they perceive as powerful. This remains the case despite new mechanisms of communication, such as the Internet, that make connecting (in a purely functional sense) much easier and less expensive.

Integrity constraints have proved fundamentally important in database management. The ID/IDREF mechanism provided by XML DTDs relies on a simple form of constraints to describe references. Yet, this mechanism is sufficient neither for specifying references in XML documents, nor for expressing semantic constraints commonly found in databases. In this paper, we extend XML DTDs with several classes of integrity constraints and investigate the complexity of reasoning about these constraints. The constraints range over keys, foreign keys, inverse constraints as well as ID constraints for capturing the semantics of object identities. They improve semantic specifications and provide a better reference mechanism for native XML applications. They are also useful in information exchange and data integration for preserving the semantics of data originating in relational and object-oriented databases. We establish complexity and axiomatization results for the (finite) implication problems associated with these constraints. In addition, we study implication of more general constraints, such as functional, inclusion and inverse constraints defined in terms of navigation paths.

This work has its roots in the HP Labs Cooltown project, whose core principle is that the integration of our physical world with the Web offers unique opportunities to enable ubiquitous computing applications. This paper describes our latest results in building a model and a software architecture called the Web presence manager (WPM) to support this physical-virtual integration. This software layer implements and specifies the services and information provided by Web representations of physical entities such as people, places, or things. We detail an extensive context-enhanced media-oriented application built on top of our platform. Our application enables mobile and context-aware access to personal contents and rendering on local appliances in a variety of ubiquitous computing environments.

The convergence of Web technology, wireless networks, and portable client devices provides new design opportunities for computer/communications systems. In the HP Labs' "Cooltown" project we have been exploring these opportunities through an infrastructure to support "web presence" for people, places and things. We put web servers into things like printers and put information into web servers about things like artwork; we group physically related things into places embodied in web servers. Using URLs for addressing, physical URL beaconing and sensing of URLs for discovery, and localized web servers for directories, we can create a location-aware but ubiquitous system to support nomadic users. On top of this infrastructure we can leverage Internet connectivity to support communications services. Web presence bridges the World Wide Web and the physical world we inhabit, providing a model for supporting nomadic users without a central control point.

This paper examines the performance of search engines over time. The performance is not as expected: search engines loose information, relevant URLs that were retrieved at a given time by a certain search engine, were not retrieved by the same search engine at a later time, although they continued to exist and to be relevant. A closer examination of the these URLs revealed that not only URLs were dropped, but content was also lost for a large portion of these URLs: no other URL retrieved by the search engine contained the same information. As far as we know this aspect of the performance of search engines has not been thoroughly studied before. The problem is investigated through a case study, using the search phrase "informetrics OR informetric". The searches were carried out in one month intervals during a five months period between January and June 1998. An additional search round and comparison were carried out on June 1999. The six largest search engines at the time were examined.

Search engines are an important tool for information foraging on the web. The broad details of how they work is, therefore, of relevance to both information seekers and providers. Yet search engines are known to only index a fraction of the web, up to a maximum of 16% in one recent study. A search engine must crawl the web periodically in order to maintain an up to date index, but, given the limitations of total coverage, how can it decide which sites to cover and which to ignore? One answer lies in research showing the importance of web links in identifying useful sources of information. This paper reports on an experiment to investigate the effect of link count on the indexing of 1000 sites in three search portals over a period of seven months. It was found that, although all engines added sites during the period of the survey, only Google showed evidence of being very responsive to the existence of links on the test site, whereas AltaVista's results were very stable over time.

In this paper, we study how linking mechanisms contribute to the expressiveness of hypertext systems. For this purpose, we formalize hypertext systems as abstract machines. As the primary benefit of hypertext systems is to be able to read documents non-linearly, their expressiveness is defined in terms of the ability to follow links. Then, we classify hypertext systems according to the power of the underlying automaton. The model allows us to compare embedded versus separate links and simple versus generic links. Then, we investigate history mechanisms, adaptive hypertexts and functional links. Our conclusion is that simple links, whether embedded or separate, generic links and some adaptive links all give hypertext systems the power of finite state automata. The history mechanism confers to them the power of pushdown automata, whereas the general functional links give them Turing completeness.

We consider the problem of node positioning in ad hoc networks. We propose a distributed, infrastructure-free positioning algorithm that does not rely on GPS (Global Positioning System). Instead, the algorithm uses the distances between the nodes to build a relative coordinate system in which the node positions are computed in two dimensions. Despite the distance measurement errors and the motion of the nodes, the algorithm provides sufficient location information and accuracy to support basic network functions. Examples of applications where this algorithm can be used include Location Aided Routing and Geodesic Packet Forwarding. Another example are sensor networks, where mobility is less of a problem. The main contribution of this work is to define and compute relative positions of the nodes in an ad hoc network without using GPS. We further explain how the proposed approach can be applied to wide area ad hoc networks.

This paper discusses the issues involved in designing a query language for the Semantic Web and presents the OWL Query Language (OWL-QL) as a candidate standard language and protocol for query-answering dialogues among Semantic Web computational agents using knowledge represented in the W3C's Ontology Web Language (OWL). OWL-QL is a formal language and precisely specifies the semantic relationships among a query, a query answer, and the knowledge base(s) used to produce the answer. Unlike standard database and Web query languages, OWL-QL supports query-answering dialogues in which the answering agent may use automated reasoning methods to derive answers to queries, as well as dialogues in which the knowledge to be used in answering a query may be in multiple knowledge bases on the Semantic Web, and/or where those knowledge bases are not specified by the querying agent. In this setting, the set of answers to a query may be of unpredictable size and may require an unpredictable amount of time to compute.

This paper describes Bibster, a Peer-to-Peer system for exchanging bibliographic metadata among researchers. We show how Bibster exploits ontologies in data-representation, query formulation, query routing, and query result presentation. The Bibster system is freely available and is used by researchers across multiple organizations.

The OWL Web Ontology Language is a new formal language for representing ontologies in the Semantic Web. OWL has features from several families of representation languages, including primarily Description Logics and frames. OWL also shares many characteristics with RDF, the W3C base of the Semantic Web. In this paper we discuss how the philosophy and features of OWL can be traced back to these older formalisms, with modifications driven by several other constraints on OWL. Several interesting problems have arisen where these influences on OWL have clashed.

We investigate machine learning methods for automatically integrating objects from different taxonomies into a master taxonomy. This problem is not only currently pervasive on the Web, but is also important to the emerging Semantic Web. A straightforward approach to automating this process would be to build classifiers through machine learning and then use these classifiers to classify objects from the source taxonomies into categories of the master taxonomy. However, conventional machine learning algorithms totally ignore the availability of the source taxonomies. In fact, source and master taxonomies often have common categories under different names or other more complex semantic overlaps. We introduce two techniques that exploit the semantic overlap between the source and master taxonomies to build better classifiers for the master taxonomy. The first technique, Cluster Shrinkage, biases the learning algorithm against splitting source categories by making objects in the same category appear more similar to each other. The second technique, Co-Bootstrapping, tries to facilitate the exploitation of inter-taxonomy relationships by providing category indicator functions as additional features for the objects. Our experiments with real-world Web data show that these proposed add-on techniques can enhance various machine learning algorithms to achieve substantial improvements in performance for taxonomy integration.

The interaction between components and objects in a distributed environment should be highly efficient and transparent to the application programmer. High efficiency can be achieved by improving the inter-processor communication (IPC) mechanism in micro kernels, while transparency can be achieved through interface definition languages (IDLs). Different encoding mechanisms like Extended Data Representation (XDR), Network Data Representation (NDR) and Common Data Representation (CDR) facilitate inter-component communication transparently and efficiently. Marshalling procedures convert data in local machine representation into common network representations. Common Object Request Broker Architecture (CORBA) uses CDR representation to encode data. This paper proposes certain changes that can be incorporated in the CDR encoding mechanism, to achieve better efficiency in transmission. The changes include the following: A bit representation for the boolean array; Removing data alignment at word boundaries; Exact allocation of send and receive buffer space depending on the data type being transmitted; Adopting inlining mechanism for some primitive data types to improve efficiency.

Current standards for SOAP, WSDL, and UDDI have no explicit support for the versioning and deprecation of Web services. This article introduces a means for Web service versioning and deprecation that is lightweight and flexible, and requires minimal development effort.

Schema matching is a basic problem in many database application domains, such as data integration, E-business, data warehousing, and semantic query processing. In current implementations, schema matching is typically performed manually, which has significant limitations. On the other hand, previous research papers have proposed many techniques to achieve a partial automation of the match operation for specific application domains. We present a taxonomy that covers many of these existing approaches, and we describe the approaches in some detail. In particular,we distinguish between schema-level and instance-level, element-level and structure-level, and language-based and constraint-based matchers. Based on our classification we review some previous match implementations thereby indicating which part of the solution space they cover.We intend our taxonomy and review of past work to be useful when comparing different approaches to schema matching, when developing a new match algorithm, and when implementing a schema matching component.

XML is rapidly emerging as a standard for exchanging business data on the World Wide Web. For the foreseeable future, however, most business data will continue to be stored in relational database systems. Consequently, if XML is to fulfill its potential, some mechanism is needed to publish relational data as XML documents. Towards that goal, one of the major challenges is finding a way to efficiently structure and tag data from one or more tables as a hierarchical XML document. Different alternatives are possible depending on when this processing takes place and how much of it is done inside the relational engine. In this paper, we characterize and study the performance of these alternatives. Among other things, we explore the use of new scalar and aggregate functions in SQL for constructing complex XML documents directly in the relational engine. We also explore different execution plans for generating the content of an XML document. The results of an experimental study show that constructing XML documents inside the relational engine can have a significant performance benefit. Our results also show the superiority of having the relational engine use what we call an "outer union plan" to generate the content of an XML document.

Collaborative tagging describes the process by which many users add metadata in the form of keywords to shared content. Recently, collaborative tagging has grown in popularity on the web, on sites that allow users to tag bookmarks, photographs and other content. In this paper we analyze the structure of collaborative tagging systems as well as their dynamical aspects. Specifically, we discovered regularities in user activity, tag frequencies, kinds of tags used, bursts of popularity in bookmarking and a remarkable stability in the relative proportions of tags within a given URL. We also present a dynamical model of collaborative tagging that predicts these stable patterns and relates them to imitation and shared knowledge.

In this paper, the development of knowledge management (KM) was surveyed, using a literature review and classification of articles from 1995 to 2004. With a keyword index and article abstract, we explored how KM performance evaluation has developed during this period. Based on a scope of 108 articles from 80 academic KM journals (retrieved from six online databases), we surveyed and classified methods of KM measurement, using the following eight categories: qualitative analysis, quantitative analysis, financial indicator analysis, non-financial indicator analysis, internal performance analysis, external performance analysis, project-orientated analysis and organization-orientated analysis, together with their measurement matrices for different research and problem domains. Future development directions for KM performance evaluation are presented in our discussion. They include: (1) KM performance measurements have tended towards expertise orientation, while evaluation development is a problem-orientated domain; (2) different information technology methodologies, such as expert systems, knowledge-based systems and case-based reasoning may be able to evaluate KM as simply another methodology; (3) the ability to continually change and obtain new understanding is the driving power behind KM methodologies, and should be the basis of KM performance evaluations in the future.

Vannevar Bush's famous paper "As We May Think" (1945) described an imaginary information retrieval machine, the Memex. The Memex is usually viewed, unhistorically, in relation to subsequent developments using digital computers. This paper attempts to reconstruct the little-known background of information retrieval in and before 1939 when "As We May Think" was originally written. The Memex was based on Bush's work during 1938-1940 developing an improved photoelectric microfilm selector, an electronic retrieval technology pioneered by Emanuel Goldberg of Zeiss Ikon, Dresden, in the 1920s. Visionary statements by Paul Otlet (1934) and Walter Schuermeyer (1935) and the development of electronic document retrieval technology before Bush are examined.

This article presents European documentalist, critical modernist, and Autonomous Marxist influenced post-Fordist views regarding the management of knowledge in mid- and late twentieth century Western modernity and postmodernity, and the complex theoretical and ideological debates, especially concerning issues of language and community. The introduction and use for corporate, governmental, and social purposes of powerful information and communication technologies created conceptual and political tensions and theoretical debates. In this article, knowledge management, including the specific recent approach known as "Knowledge Management", is discussed as a social, cultural, political, and organizational issue, including the problematic feasibility of capturing and representing knowledge that is "tacit," "invisible," and is imperfectly representable. "Social capital" and "affective labor" are discussed as elements of "tacit" knowledge. Views of writers in the European documentalist, critical modernist, and Italian Autonomous Marxist influenced post-Fordist traditions, such as Otlet, Briet, Heidegger, Benjamin, Marazzi, and Negri, are discussed.

This study introduces methods for evaluating search engine performance over a time period. Several measures are defined, which as a whole describe search engine functionality over time. The necessary setup for such studies is described, and the use of these measures is illustrated through a specific example. The set of measures introduced here may serve as a guideline for the search engines for testing and improving their functionality. We recommend setting up a standard suite of measures for evaluating search engine performance.

XML is successful as a machine processable data interchange format, but it is often too verbose for human use. For this reason, many XML languages permit an alternative more legible non-XML syntax. XSLT stylesheets are often used to convert from the XML syntax to the alternative syntax; however, such transformations are not reversible since no general tool exists to automatically parse the alternative syntax back into XML. We present XSugar, which makes it possible to manage dual syntax for XML languages. An XSugar specification is built around a context-free grammar that unifies the two syntaxes of a language. Given such a specification, the XSugar tool can translate from alternative syntax to XML and vice versa. Moreover, the tool statically checks that the transformations are reversible and that all XML documents generated from the alternative syntax are valid according to a given XML schema.

The original Scientific American article on the Semantic Web appeared in 2001. It described the evolution of a Web that consisted largely of documents for humans to read to one that included data and information for computers to manipulate. The Semantic Web is a Web of actionable information — information derived from data through a semantic theory for interpreting the symbols. This simple idea, however, remains largely unrealized. Shopbots and auction bots abound on the Web, but these are essentially handcrafted for particular tasks; they have little ability to interact with heterogeneous data and information types. Because we haven't yet delivered large-scale, agent-based mediation, some commentators argue that the Semantic Web has failed to deliver. We argue that agents can only flourish when standards are well established and that the Web standards for expressing shared meaning have progressed steadily over the past five years. Furthermore, we see the use of ontologies in the e-science community presaging ultimate success for the Semantic Web — just as the use of HTTP within the CERN particle physics community led to the revolutionary success of the original Web. This article is part of a special issue on the Future of AI.

This paper introduces the notion of context-aware mobile hypermedia. Context awareness means to take the users' context such as location, time, objective, community relations, etc., into account when browsing, searching, annotating, and linking. Attributes constituting the context of the user may be sensed automatically and/or be provided by the user directly. When mobile, the user may obtain context-aware hypermedia support on a variety of small and medium sized computing platforms such as mobile phones, PDAs, tablet PCs, and laptops. This paper introduces the HyCon (HyperContext) framework with an architecture for context-aware hypermedia. The architecture includes interfaces for a sensor tier encapsulating relevant sensors and represents the hypermedia objects in structures based on the XLink and RDF standards. A prototype called the HyConExplorer created with the framework is presented, and it is illustrated how the classical hypermedia features such as browsing, searching, annotating, linking, and collaboration are supported in context-aware hypermedia. Among the features of the HyConExplorer are real-time location-based searches via Google collecting hits within a specified nimbus around the user's GPS position. Finally, the use of scenarios for and evaluation of the use of the HyConExplorer in public school projects are discussed.

The Standard Generalized Markup Language (SGML) and the Extensible Markup Language (XML) allow authors to better transmit the semantics in their documents by explicitly specifying the relevant structures in a document or class of documents by means of document type definitions (DTDs). Several authors have proposed to regard DTDs as extended context-free grammars expressed in a notation similar to extended Backus-Naur form. In addition, the SGML standard allows the semantics of content models (the right-hand side of productions) to be modified by exceptions. Inclusion exceptions allow named elements to appear anywhere within the content of a content model, and exclusion exceptions preclude named elements from appearing in the content of a content model. Since XML does not allow exceptions, the problem of exception removal has received much interest recently. Motivated by this, Kilpeläinen and Wood have proved that exceptions do not increase the expressive power of extended context-free grammars and that for each DTD with exceptions, we can obtain a structurally equivalent extended context-free grammar. Since their argument was based on an exponential simulation, they also conjectured that an exponential blow-up in the size of the grammar is a necessary devil when purging exceptions away. We prove their conjecture under the most realistic assumption that NP-complete problems do not admit non-uniform polynomial-time algorithms. Kilpeläinen and Wood also asked whether the parsing problem for extended context-free grammars with exceptions admits efficient algorithmic solution. We show the NP-completeness of the very basic problem: given a string w and a context-free grammar G (not even extended) with exclusion exceptions (no inclusion exceptions needed), decide whether w belongs to the language generated by G. Our results and arguments point up the limitations of using extended context-free grammars as a model of SGML, especially when one is interested in understanding issues related to exceptions.

World Wide Web authors must cope in a hypermedia environment analogous to second-generation computing languages, building and managing most hypermedia links using simple anchors and single-step navigation. Following this analogy, sophisticated application environments on the World Wide Web will require third- and fourth-generation hypermedia features. Implementing third- and fourth-generation hypermedia involves designing both high-level hypermedia features and the high-level authoring environments system developers build for authors to specify them. We present a set of high-level hypermedia features including typed nodes and links, link attributes, structure-based query, transclusions, warm and hot links, private and public links, hypermedia access permissions, computed personalized links, external link databases, link update mechanisms, overviews, trails, guided tours, backtracking, and history-based navigation. We ground our discussion in the hypermedia research literature, and illustrate each feature both from existing implementations and a running scenario. We also give some direction for implementing these on the World Wide Web and in other information systems.

With unit cost falling as the number of components per circuit rises, by 1975 economics may dictate squeezing as many as 65'000 components on a single silicon chip

Web applications produce data at colossal rates, and those rates compound every year as the Web becomes more central to our lives. Other data sources such as environmental monitoring and location-based services are a rapidly expanding part of our day-to-day experience. Even as throughput is increasing, users and business owners expect to see their data with ever-decreasing latency. Advances in computer hardware (cheaper memory, cheaper disks, and more processing cores) are helping somewhat, but not enough to keep pace with the twin demands of rising throughput and decreasing latency.

The Extensible Markup Language (XML), which just celebrated its 10th birthday, is one of the big success stories of the Web. Apart from basic Web technologies (URIs, HTTP, and HTML) and the advanced scripting driving the Web 2.0 wave, XML is by far the most successful and ubiquitous Web technology. With great power, however, comes great responsibility, so while XML's success is well earned as the first truly universal standard for structured data, it must now deal with numerous problems that have grown up around it. These are not entirely the fault of XML itself, but instead can be attributed to exaggerated claims and ideas of what XML is and what it can do.

Over the span of a few years, CORBA moved from being a successful middleware that was hailed as the Internet's next-generation e-commerce infrastructure to being an obscure niche technology that is all but forgotten. This rapid decline is surprising. How can a technology that was produced by the world's largest software consortium fall from grace so quickly? Many of the reasons are technical: poor architecture, complex APIs, and lack of essential features all contributed to CORBA's downfall. However, such technical shortcomings are a symptom rather than a cause. Ultimately, CORBA failed because its standardization process virtually guarantees poor technical quality. Seeing that other standards consortia use a process that is very similar, this does not bode well for the viability of other technologies produced in this fashion.

XML Schema is now 5 years old, having matured from a newborn into an active youngster. So what have we learned about this young one's personality? We've always known it was complex. Indeed, the original debate about whether to make it a Recommendation indicated concern. (See Last Word and Questionnaire.) This rich toolset has caused schema designers to wonder which features they should or should not use. If we analyze what people are actually implementing, perhaps we can glean some guidance. I decided to embark on a quest to see if we can put together a profile of XML Schema based on experiences thus far.

XML Schema is a very powerful and also a rather complex schema language. One of the problems when working with XML Schema is the fact that XML Schema uses an XML syntax, which makes XML Schemas verbose and hard to read. In this article, we describe a compact text-based syntax for XML Schema, called XML Schema Compact Syntax (XSCS), which re-uses well known syntactic constructs from DTDs; and we present a Java-based implementation for converting the compact syntax to the XML syntax and vice versa.

In this article, a small schema language for XML is presented which can be used to restrict the use of character repertoires in XML documents. It is called Character Repertoire Validation for XML (CRVX). CRVX restrictions can be based on structural components of an XML document, contexts, or a combination of both.

Assembling various parts of a document before processing the assembled document is a recurring theme in document processing. XML Inclusions (XInclude) is the W3C standard which has been created to support this scenario, but since it is a standalone specification, it needs to be supported by a piece of software implementing this functionality. The XInclude Processor (XIPr) written in XSLT 2.0 implements XInclude and thus may help to reduce the dependency on numerous software packages, if XInclude should be used in an environment where XSLT 2.0 is used anyway. XIPr is implemented as a single XSLT 2.0 stylesheet and can be used standalone in a publishing pipeline, or as an imported module in some other XSLT code for integrated XInclude processing.

XML Schema bietet im Gegensatz zu DTDs eine Vielzahl an Modellierungsfeatures und damit realisierbaren Varianten. Oft ist nicht klar, auf welche Weise ein gegebenes Modell am besten als XML Schema umgesetzt werden sollte. In diesem und einem nachfolgenden Artikel wird deshalb der Frage nachgegangen, welche Varianten es gibt, wie sie sich unterscheiden, was ihre Vor- und Nachteile sind, und wie sie sich insbesondere unter dem Blickpunkt der Wiederverwendung und Erweiterbarkeit bewerten lassen.

XML bietet verschiedene Möglichkeiten, erweiterbare Datenstrukturen zu definieren und zu verwenden, aber es bleibt dennoch der Umsicht und vor allem der Planung von Designern überlassen, XML tatsächlich so zu verwenden, dass es diese Vorteile ausspielen kann. In diesem Artikel betrachten wir, wieso Erweiterbarkeit bei der Verwendung von XML ein wichtiger Aspekt ist, und wie sich diese Erweiterbarkeit mit XML Schema erreichen lässt. Als weiteren Aspekt betrachten wir die Offenheit eines Schemas, also die Frage, inwieweit ein Schema Erweiterungen in Dokumenten zulässt.

Für die Versionierung von XML Schemas ist es notwendig, sich Gedanken über den Umgang mit Versionen zu machen, und zwar aus zweierlei Sicht. Die erste Sicht ist die des Schema-Entwickler, dem sich die Frage stellt, wie er die Namespaces handhabt, die für die verschiedenen Schemas verwendet werden. Die andere Sicht ist die der Software-Entwickler, die in ihre Software Wissen darum einbauen müssen, wie mit Instanzen verschiedener Versionen umgegangen wird. Beide Sichten sollten gemeinsam dazu beitragen, ein möglichst robustes und flexibles Szenario zu implementieren, in dem verschiedene Schemaversionen koexistieren können.

XML bietet zwar durchaus das allgemein akzeptierte Verfahren zum Austausch strukturierter Daten, das in vielen Anwendungen benötigt wird, ist aber dennoch nicht ausreichend, Interoperabilität zwischen Anwendungen sicherzustellen. Probleme können auf vielen verschiedenen Ebenen entstehen, beginnend bei so grundlegenden Dingen wie Zeichencodierungen, bis hin zu Problemen des inhaltlichen Verständnisses von XML Dokumenten. Im vorliegenden Artikel soll auf den letzteren Aspekt näher eingegangen werden, also die Frage, was notwendig ist, damit der Austausch von XML nicht nur syntaktisch funktioniert, sondern auch auf einem gemeinsamen Verständnis beider Seiten basiert.

We consider XML documents described by a document type definition (DTD). An XML-grammar is a formal grammar that captures the syntactic features of a DTD. We investigate properties of this family of grammars. We show that every XML-language basically has a unique XML-grammar. We give two characterizations of languages generated by XML-grammars, one is set-theoretic, the other is by a kind of saturation property. We investigate decidability problems and prove that some properties that are undecidable for general context-free languages become decidable for XML-languages. We also characterize those XML-grammars that generate regular XML-languages.

Within the information systems field, the task of conceptual modeling involves building a representation of selected phenomena in some domain. High-quality conceptual modeling work is important because it facilitates early detection and correction of system development errors. It also plays an increasingly important role in activities like business process reengineering and documentation of best-practice data and process models in enterprise resource planning systems. Yet little research has been undertaken on many aspects of conceptual modeling. In this paper, we propose a framework to motivate research that addresses the following fundamental question: How can we model the world to better facilitate our developing, implementing, using, and maintaining more valuable information systems? The framework comprises four elements: conceptual-modeling grammars, conceptual-modeling methods, conceptual-modeling scripts, and conceptual-modeling contexts. We provide examples of the types of research that have already been undertaken on each element and illustrate research opportunities that exist.

Large scale research Digital Libraries (DLs) have a large array of potentially useful metadata. Yet, many popular DLs do not provide a convenient way to navigate the metadata or to visualize classification schema in the user session. For example, in the broad world of Management Information Systems (MIS) research, a high-level overview of MIS topics and their interrelationships would be useful to navigate a MIS DL before zooming in on a specific article. To address this obstacle, this paper describes a prototype, the Technical Report Visualizer System (TRV), which uses a wide variety of open standards to expose DL classification metadata in the navigation interface. The system captures MIS article metadata from the Open Archives Initiative (OAI) compliant arXiv e-Print archive at Cornell University. The OAI Protocol for Metadata Harvesting (OAI-PMH) is used to collect the topic metadata; the articles' Association for Computing Machinery's (ACM) Computing Classification System codes. We display the topic metadata in a Java hyperbolic tree and make use of XML conceptual product and implementation product standards and specifications, such as the Dublin Core and BiblioML bibliographic metadata sets, XML Topic Maps, Xalan and Xerces, to link user navigation activity to the abstracts and full text contents of the articles. We discuss the flexibility and convenience of XML standards and link this effort to related digital library visualization approaches.

We propose two new tools to address the evolution of hyperlinked corpora. First, we define time graphs to extend the traditional notion of an evolving directed graph, capturing link creation as a point phenomenon in time. Second, we develop definitions and algorithms for time-dense community tracking, to crystallize the notion of community evolution. We develop these tools in the context of Blogspace, the space of weblogs (or blogs). Our study involves approximately 750 K links among 25 K blogs. We create a time graph on these blogs by an automatic analysis of their internal time stamps. We then study the evolution of connected component structure and microscopic community structure in this time graph. We show that Blogspace underwent a transition behavior around the end of 2001, and has been rapidly expanding, not just in metrics of scale but also in metrics of community structure and connectedness. By randomizing link destinations in Blogspace, but retaining sources and timestamps, we introduce a concept of randomized Blogspace. Herein, we observe similar evolution of a giant component, but no corresponding increase in community structure. Having demonstrated the formation of micro-communities over time, we then turn to the ongoing activity within active communities. We extend recent work of Kleinberg (2002) to discover dense periods of "bursty" intra-community link creation. Furthermore, we find that the blogs that give rise to these communities are significantly more enduring than an average blog.

Most documents available over the Web conform to the HTML specification. Such documents are hierarchically structured in nature. The existing data models for the Web either fail to capture the hierarchical structure within the documents or can only provide a very low level representation of such hierarchical structure. How to represent and query HTML documents at a higher level is an important issue. In this paper, we first propose a novel conceptual model for HTML. This conceptual model has only a few simple constructs but is able to represent the complex hierarchical structure within HTML documents at a level that is close to human conceptualization/visualization of the documents. We also describe how to convert HTML documents based on this conceptual model. Using the conceptual model and conversion method, one can capture the essence (i.e., semistructure) of HTML documents in a natural and simple way. Based on this conceptual model, we then present a rule?based language to query HTML documents over the Internet. This language provides a simple but very powerful way to query both intra?document structures and inter?document structures and allows the query results to be restructured. Being rule?based, it naturally supports negation and recursion and therefore is more expressive than SQL?based languages. A logical semantics is also provided.

Links are the key element for changing a text into a hypertext, and yet the WWW provides limited linking facilities. Modeled on Open Hypermedia research the Distributed Link Service provides an independent system of link services for the World Wide Web and allows authors to create configurable navigation pathways for collections of WWW resources. This is achieved by adding links to documents as they are delivered from a WWW server, and by allowing the users to choose the sets of links that they will see according to their interests. This paper describes the development of the link service, the facilities that it adds for users of the WWW and its specific use in an Electronic Libraries project.

Today's Web sites are intricate but not intelligent; while Web navigation is dynamic and idiosyncratic, all too often Web sites are fossils cast in HTML. In response, this paper investigates adaptive Web sites: sites that automatically improve their organization and presentation by learning from visitor access patterns. Adaptive Web sites mine the data buried in Web server logs to produce more easily navigable Web sites. To demonstrate the feasibility of adaptive Web sites, the paper considers the problem of index page synthesis and sketches a solution that relies on novel clustering and conceptual clustering techniques. Our preliminary experiments show that high-quality candidate index pages can be generated automatically, and that our techniques outperform existing methods (including the Apriori algorithm, K-means clustering, hierarchical agglomerative clustering, and COBWEB) in this domain.

Considerations and techniques are proposed that reduce the complexity of programs by dividing them into functional modules. This can make it possible to create complex systems from simple, independent, reusable modules. Debugging and modifying programs, reconfiguring I/O devices, and managing large programming projects can all be greatly simplified. And, as the module library grows, increasingly sophisticated programs can be implemented using less and less new code.

This paper relates our experiences at the University of California, Berkeley (UC Berkeley), designing a service science discipline. We wanted to design a discipline of service science in a principled and theoretically motivated way. We began our work by asking, "What questions would a service science have to answer?" and from that we developed a new framework for understanding service science. This framework can be visualized as a matrix whose rows are stages in a service life cycle and whose columns are disciplines that can provide answers to the questions that span the life cycle. This matrix systematically organizes the issues and challenges of service science and enables us to compare our model of a service science discipline with other definitions and curricula. This analysis identified gaps, overlaps, and opportunities that shaped the design of our curriculum and in particular a new survey course that serves as the cornerstone of service science education at UC Berkeley.

In this paper we describe our efforts at the Massachusetts Institute of Technology Media Laboratory toward realizing an electronic book comprised of hundreds of electronically addressable display pages printed on real paper substrates. Such pages may be typeset in situ, thus giving such a book the capability to be any book. We outline the technology we are developing to bring this about and describe a number of applications that such a device enables.

Most business data are stored in relational database systems, and SQL (Structured Query Language) is used for data retrieval and manipulation. With XML (Extensible Markup Language) rapidly becoming the de facto standard for retrieving and exchanging data, new functionality is expected from traditional databases. Existing SQL applications will evolve to retrieve relational data as XML data using database or SQL extensions for XML. New XML data will be stored, searched, and manipulated in the database as a "first class" citizen along with existing relational data. Furthermore, new applications will emerge that solely operate in terms of XML. These new XML applications operate on the same database using an XML query language, XQuery. In this paper, we describe an integrated database architecture that enables SQL applications with XML extensions as well as XQuery applications to operate on the same data. The architecture allows for a seamless flow from relational data to XML and back.

With the widespread adoption of SOAP and Web services, XML-based processing, and parsing of XML documents in particular, is becoming a performance-critical aspect of business computing. In such scenarios, XML is often constrained by an XML Schema grammar, which can be used during parsing to improve performance. Although traditional grammar-based parser generation techniques could be applied to the XML Schema grammar, the expressiveness of XML Schema does not lend itself well to the generic intermediate representations associated with these approaches. In this paper we present a method for generating efficient parsers by using the schema component model itself as the representation of the grammar. We show that the model supports the full expressive power of the XML Schema, and we present results demonstrating significant performance improvements over existing parsers.

Extensible Markup Language (XML) has grown rapidly over the last decade to become the de facto standard for heterogeneous data exchange. Its popularity is due in large part to the ease with which diverse kinds of information can be represented as a result of the self-describing nature and extensibility of XML itself. The ease and speed with which information can be represented does not extend, however, to exchanging such information between autonomous sources. In the absence of controlling standards, such sources will typically choose differing XML representations for the same concept, and the actual exchange of information between them requires that the representation produced by one source be transformed into a representation understood by the other. Creating this information exchange "glue" is a tedious and error-prone process, whether expressed as Extensible Stylesheet Language Transformation (XSLT), XQuery, Java, Structured Query Language (SQL), or some other format. In this paper, we present an extensible XML mapping architecture that elevates XML mapping technology to a fundamental integration component that promotes code generation, mapping reuse, and mapping as metadata.

Although the Extensible Markup Language (XML) has gained in popularity and has resulted in the creation of powerful software for authoring, transforming, and querying XML-based business data, much information remains in non-XML form. In this paper we introduce an approach to virtualize data resources and thus enable applications to access both XML and non-XML sources. We describe the architectural components that enable virtual XML — a toolbox that includes a cursor model, an XML-view mechanism such as the view created with the Data Format Description Language (DFDL), and XML processing languages. We illustrate the applicability of virtual XML through a number of use cases in various environments. We discuss the products that we expect from vendors and the open-source community and the way enterprises can plan to take advantage of virtual XML developments. Finally, we outline future research directions that include a vision of virtual XML that covers large-scale structures such as entire file systems, databases, or even the World Wide Web.

The topic of Computer Supported Cooperative Work (CSCW) has attracted much attention in the last few years. While the field is obviously still in the process of development, there is a marked ambiguity about the exact focus of the field. This lack of focus may hinder its further development and lead to its dissipation. In this paper we set out an approach to CSCW as a field of research which we believe provides a coherent conceptual framework for this area, suggesting that it should be concerned with the support requirements of cooperative work arrangements. This provides a more principled, comprehensive, and, in our opinion, more useful conception of the field than that provided by the conception of CSCW as being focused on computer support for groups. We then investigate the consequences of taking this alternative conception seriously, in terms of research directions for the field. As an indication of the fruits of this approach, we discuss the concept of 'articulation work' and its relevance to CSCW. This raises a host of interesting problems that are marginalized in the work on small group support but critical to the success of CSCW systems 'in the large', i. e., that are designed to meet current work requirements in the everyday world.

The string-to-string correction problem is to determine the distance between two strings as measured by the minimum cost sequence of "edit operations" needed to change the one string into the other. The edit operations investigated allow changing one symbol of a string into another single symbol, deleting one symbol from a string, or inserting a single symbol into a string. An algorithm is presented which solves this problem in time proportional to the product of the lengths of the two strings. Possible applications are to the problems of automatic spelling correction and determining the longest subsequence of characters common to two strings.

We study the complexity of two central XML processing problems. The first is XPath 1.0 query processing, which has been shown to be in PTIME in previous work. We prove that both the data complexity and the query complexity of XPath 1.0 fall into lower (highly parallelizable) complexity classes, while the combined complexity is PTIME-hard. Subsequently, we study the sources of this hardness and identify a large and practically important fragment of XPath 1.0 for which the combined complexity is LOGCFL-complete and, therefore, in the highly parallelizable complexity class NC2. The second problem is the complexity of validating XML documents against various typing schemes like Document Type Definitions (DTDs), XML Schema Definitions (XSDs), and tree automata, both with respect to data and to combined complexity. For data complexity, we prove that validation is in LOGSPACE and depends crucially on how XML data is represented. For the combined complexity, we show that the complexity ranges from LOGSPACE to LOGCFL, depending on the typing scheme.

Structured document databases can be naturally viewed as derivation trees of a context-free grammar. Under this view, the classical formalism of attribute grammars becomes a formalism for structured document query languages. From this perspective, we study the expressive power of BAGs: Boolean-valued attribute grammars with propositional logic formulas as semantic rules, and RAGs: relation-valued attribute grammars with first-order logic formulas as semantic rules. BAGs can express only unary queries; RAGs can express queries of any arity. We first show that the (unary) queries expressible by BAGs are precisely those definable in monadic second-order logic. We then show that the queries expressible by RAGs are precisely those definable by first-order inductions of linear depth, or, equivalently, those computable in linear time on a parallel machine with polynomially many processors. Further, we show that RAGs that only use synthesized attributes are strictly weaker than RAGs that use both synthesized and inherited attributes. We show that RAGs are more expressive than monadic second-order logic for queries of any arity. Finally, we discuss relational attribute grammars in the context of BAGs and RAGs. We show that in the case of BAGs this does not increase the expressive power, while different semantics for relational RAGs capture the complexity classes NP, coNP and the intersection of UP and coUP.

This paper discusses interoperability of digital rights management (DRM) systems. We start by describing a basic reference model for DRM. The cause of interoperability is served by understanding and circumscribing what DRM is "in the whole." Then we outline and contrast three different approaches to achieving interoperability. One approach relies on flexible network services to provide functionality where it is needed, perhaps by bridging different systems. We describe an experimental service orchestration system (NEMO) that enables such an approach.

Back in 1995, Netscape co-founder Marc Andreessen predicted that his fledgling Web browser would one day render Windows obsolete. Fifteen years later, Netscape is long gone, and the traditional desktop operating system (OS) remains firmly established on most personal computers. Meanwhile, Web browsers still look a lot like they did in the mid-1990s, running inside application windows. In hindsight, Andreessen may have spoken a bit too soon. But history may yet prove him right.

We all know the scene: It is the basement of an apartment building and the lights are dim. The man is wearing a trench coat and a fedora pulled down low to hide his face. Between the hat and the coat we see headphones, and he appears to be listening intently to the output of a set of alligator clips attached to a phone line. He is a detective eavesdropping on a suspect's phone calls. This is wiretapping?as it was in the film noir era of 1930s Hollywood. It doesn't have much to do with modern electronic eavesdropping, which is about bits, packets, switches, and routers.

Many Web sites embed third-party content in frames, relying on the browser's security policy to protect against malicious content. However, frames provide insufficient isolation in browsers that let framed content navigate other frames. We evaluate existing frame navigation policies and advocate a stricter policy, which we deploy in the open-source browsers. In addition to preventing undesirable interactions, the browser's strict isolation policy also affects communication between cooperating frames. We therefore analyze two techniques for interframe communication between isolated frames. The first method, fragment identifier messaging, initially provides confidentiality without authentication, which we repair using concepts from a well-known network protocol. The second method, postMessage, initially provides authentication, but we discover an attack that breaches confidentiality. We propose improvements in the postMessage API to provide confidentiality; our proposal has been standardized and adopted in browser implementations.

Many Web sites embed third-party content in frames, relying on the browser's security policy to protect against malicious content. However, frames provide insufficient isolation in browsers that let framed content navigate other frames. We evaluate existing frame navigation policies and advocate a stricter policy, which we deploy in the open-source browsers. In addition to preventing undesirable interactions, the browser's strict isolation policy also affects communication between cooperating frames. We therefore analyze two techniques for interframe communication between isolated frames. The first method, fragment identifier messaging, initially provides confidentiality without authentication, which we repair using concepts from a well-known network protocol. The second method, postMessage, initially provides authentication, but we discover an attack that breaches confidentiality. We propose improvements in the postMessage API to provide confidentiality; our proposal has been standardized and adopted in browser implementations.

End-user development (EUD) activities range from customization to component configuration and programming. Office software, such as the ubiquitous spreadsheet, provides customization facilities, while the growth of the Web has added impetus to end-user scripting for interactive functions in Web sites. In scientific and engineering domains, end users frequently develop complex systems with standard programming languages such as C++ and Java. However, only a minority of users adapt commercial off-the-shelf (COTS) software products. Indeed, composing systems from reusable components, such as enterprise resource planing (ERP) systems, defeats most end users who resort to expensive and scarce expert developers for implementation.

The services sector has grown over the last 50 years to dominate economic activity in most advanced industrial economies, yet scientific understanding of modern services is rudimentary. Here, we argue for a services science discipline to integrate across academic silos and advance service innovation more rapidly.

Computer scientists work with formal models of algorithms and computation, and someday service scientists may work with formal models of service systems. The four examples here document some of the early efforts to establish a new academic discipline and new profession.

The Extensible Markup Language (XML), which just celebrated its 10th birthday, is one of the big success stories of the Web. Apart from basic Web technologies (URIs, HTTP, and HTML) and the advanced scripting driving the Web 2.0 wave, XML is by far the most successful and ubiquitous Web technology. With great power, however, comes great responsibility, so while XML's success is well earned as the first truly universal standard for structured data, it must now deal with numerous problems that have grown up around it. These are not entirely the fault of XML itself, but instead can be attributed to exaggerated claims and ideas of what XML is and what it can do.

The classical approach to the data aspect of system design distinguishes conceptual, logical, and physical models. Models of each type or level are governed by metamodels that specify the kinds of concepts and constraints that can be used by each model; in most cases metamodels are accompanied by languages for describing models. For example, in database design, conceptual models usually conform to the Entity-Relationship (ER) metamodel (or some extension of it), the logical model maps ER models to relational tables and introduces normalization, and the physical model handles implementation issues such as possible denormalizations in the context of a particular database schema language. In this modeling methodology, there is a single hierarchy of models that rests on the assumption that one data model spans all modeling levels and applies to all the applications in some domain. The "one true model" approach assumes homogeneity, but this does not work very well for the Web. The Web as a constantly growing ecosystem of heterogeneous data and services has challenged a number of practices and theories about the design of IT landscapes. Instead of being governed by "one true model" used by everyone, the underlying assumption of top-down design, Web data and services evolve in an uncoordinated fashion. As a result, a fundamental challenge with Web data and services is matching and mapping local and often partial models that not only are different models of the same application domain, but also differ, implicitly or explicitly, in their associated metamodels.

The fair-use exceptions in U.S. copyright law are being undermined by rules programmed into consumer electronics and computers that reflect the exclusive interest of rights holders alone.

Research has shown that privacy policies tend to intensify privacy concerns rather than engender trust. One way to combat this dichotomy is to redesign their content, language, and presentation format.

A method for locating specific character strings embedded in character text is described and an implementation of this method in the form of a compiler is discussed. The compiler accepts a regular expression as source language and produces an IBM 7094 program as object language. The object program then accepts the text to be searched as input and produces a signal every time an embedded string in the text matches the given regular expression. Examples, problems, and solutions are also presented.

I applaud Miller's WordNet project and feel that there is much in common in our approaches, even though there are fundamental differences in the two expressions of that spirit. Here, I list the four differences I noted, closing with a crucial observation concerning the common spirit in our work.

CommerceNet's eCo System initiative, launched in 1996, aims to transform the World-Wide Web into an agent-based infrastructure for Internet commerce. Today's Web gives people unprecedented access to online information and services. But its information is delivered in format-oriented, handcrafted Hypertext Markup Language (HTML), making it understandable only through human eyes. Software agents and search engines have difficulty using the information because it is not semantically encoded. Clever programmers work around some of HTML's inherent limitations by using proprietary tags or software that "scrapes" Web pages to extract content. Unfortunately, such ad hoc approaches do not scale. Proprietary tags require browser plug-ins, and scraping approaches require a customized script for each Web site. These approaches balkanize the Web, making it inaccessible to agents.

Blogs constitute a remarkable artifact of the Web. Most people think of them as Web pages with reverse chronological sequences of dated entries, usually with sidebars of profile information and usually maintained and published with the help of a popular blog authoring tool. They tend to be quirky, highly personal, typically read by repeat visitors, and interwoven into a network of tight-knit but active communities. We refer to the collection of blogs and all their links as blogspace. By analyzing the structure and content of more than one million blogs worldwide, we've now unearthed some fascinating insights into blogger behavior.

Blogging is sometimes viewed as a new, grassroots form of journalism and a way to shape democracy outside the mass media and conventional party politics. Blog sites devoted to politics and punditry, as well as to sharing technical developments (such as www.slashdot.org), receive thousands of hits a day. But the vast majority of blogs are written by ordinary people for much smaller audiences. Here, we report the results of an ethnographic investigation of blogging in a sample of ordinary bloggers. We investigated blogging as a form of personal communication and expression, with a specific interest in uncovering the range of motivations driving individuals to create and maintain blogs.

Even though object-oriented development was introduced in the late 1960s (beginning with the Simula programming language), OO development has not yet lived up to its promises. A major stumbling block to reaping the promised benefits is learning the OO approach. One reason that learning OO is so difficult may be that we do not yet thoroughly understand the fundamental concepts that define the OO approach. When reviewing the body of work on OO development, most authors simply suggest a set of concepts that characterize OO, and move on with their research or discussion. Thus, they are either taking for granted that the concepts are known or implicitly acknowledging that a universal set of concepts does not exist. Several authors, asserting there is no clear definition of the essence of OO, have called for the development of a consensus. While a few have tried to develop such a consensus, to date a thorough review of the literature and identification of the fundamental concepts of the OO approach has been lacking. The goal of this article is twofold: to identify and describe the fundamental concepts, or quarks, of object-oriented development, and identify how these concepts fit together into a coherent scheme.

In almost all computer applications, users must enter correct words for the desired objects or actions. For success without extensive training, or in first-tries for new targets, the system must recognize terms that will be chosen spontaneously. We studied spontaneous word choice for objects in five application-related domains, and found the variability to be surprisingly large. In every case two people favored the same term with probability <0.20. Simulations show how this fundamental property of language limits the success of various design methodologies for vocabulary-driven interaction. For example, the popular approach in which access is via one designer's favorite single word will result in 80-90 percent failure rates in many common situations. An optimal strategy, unlimited aliasing, is derived and shown to be capable of several-fold improvements.

The concepts behind the five principal normal forms in relational database theory are presented in simple terms.

The human-computer interaction community aims to increase the awareness and acceptance of established methods among software practitioners. Indeed, awareness of the basic usability methods will drive an Information Society for all.

If developers are not wise with its application, SOAP may lose the ability to tunnel through firewalls — an ability that represents one of its primary advantages.

This paper discusses modularization as a mechanism for improving the flexibility and comprehensibility of a system while allowing the shortening of its development time. The effectiveness of a "modularization" is dependent upon the criteria used in dividing the system into modules. A system design problem is presented and both a conventional and unconventional decomposition are described. It is shown that the unconventional decompositions have distinct advantages for the goals outlined. The criteria used in arriving at the decompositions are discussed. The unconventional decomposition, if implemented with the conventional assumption that a module consists of one or more subroutines, will be less efficient in most cases. An alternative approach to implementation which does not have this effect is sketched.

Future users of large data banks must be protected from having to know how the data is organized in the machine (the internal representation). A prompting service which supplies such information is not a satisfactory solution. Activities of users at terminals and most application programs should remain unaffected when the internal representation of data is changed and even when some aspects of the external representation are changed. Changes in data representation will often be needed as' a result of changes in query, update, and report traffic and natural growth in the types of stored information. Existing non inferential, formatted data systems provide users with tree-structured files or slightly more general network models of the data. In Section 1, inadequacies of these models are discussed. A model based on n-ary relations, a normal form for data base relations, and the concept of a universal data sub language are introduced. In Section 2, certain operations on relations (other than logical inference) are discussed and applied to the problems of redundancy and consistency in the user's model.

An encryption method is presented with the novel property that publicly revealing an encryption key does not thereby reveal the corresponding decryption key. This has two important consequences: Couriers or other secure means are not needed to transmit keys, since a message can be enciphered using an encryption key publicly revealed by the intended recipient. Only he can decipher the message, since only he knows the corresponding decryption key. A message can be "signed" using a privately held decryption key. Anyone can verify this signature using the corresponding publicly revealed encryption key. Signatures cannot be forged, and a signer cannot later deny the validity of his signature. This has obvious applications in "electronic mail" and "electronic funds transfer" systems. A message is encrypted by representing it as a number M, raising M to a publicly specified power e, and then taking the remainder when the result is divided by the publicly specified product, n, of two large secret prime numbers p and q. Decryption is similar; only a different, secret, power d is used, where e * d = 1(mod (p - 1) * (q - 1)). The security of the system rests in part on the difficulty of factoring the published divisor, n.

In many collaborative research settings, electronic bibliographic repositories (bibliographies) are used to aggregate information about related work among researchers. These bibliographies allow for group bibliography collection, individual tracking of each user's library, and personal annotation capabilities within each user's library. However, most tools used for managing bibliographic data do not support collaboration. Given the collaborative nature of the research group, this information should be shareable between researchers within the group and potentially across larger organizational units (for example, research institutes). By using ShaRef, users can share bibliographic information and collaborate, publish and export data using a variety of output channels. ShaRef's goal is to make sharing of and collaboration with bibliographic information easier than it is today.

Personalization of services often has to cope with the conflicting goals of allowing cooperation and sharing, which require common data formats and services, and supporting individual use cases, which require as much personalization as possible. In this paper we present the ShaRef approach to personalization and sharing, which on the one hand allows users to cooperatively work with bibliographic references, and on the other hand supports the usage of this information in personalized and diverse ways. The goal of this approach is to foster as much cooperation as possible, while simultaneously supporting users with individualized ways of reusing the cooperatively managed data. This way of building applications combines the beneficial aspects of information sharing and personalization. Using this approach, applications are better suited to become building blocks in information infrastructures that are built by users in unpredictable ways.

Building hypertext systems to provide the required functionality to write hypertexts has always been a goal of hypertext research. The parallel development of hypertext research prototypes and the World Wide Web has resulted in repeated attempts to replace the Web or offer world-wide all-purpose services to augment the Web with "missing" functionality. The paper argues that focusing on the development of tools that offer support to hypertext authors for specific tasks is a necessary first step for the introduction of sophisticated hypertext features into the Web. Following a brief history of interaction with the Web, we demonstrate why authoring tools for the Web are a critical target for efforts to extend the use of hypertexts in the Web. We introduce indirect authoring as a label for a shared characteristic of different approaches that try to reduce the complexity and cognitive overhead involved in authoring hypertext. Drawing on this analysis, we lay out some consequences for hypertext research. We provide pointers to projects that have started to experiment with indirect authoring, and list immediate research questions. Developing a diversity of task-oriented authoring tools to reduce the cognitive overhead for authoring hypertexts could change the face of the Web.

Currently, the Open Hypermedia Systems (OHS) Working Group claims three main areas of interest: scenarios, reference architectures, and protocols. The discussions over scenarios of OHS use are supposed to inform the work on OHS reference architectures, which in turn is supposed to enable the development of an Open Hypermedia Protocol (OHP) that will allow clients of one OHP-compliant OHS to use services of other OHP-compliant OHS's. In this paper, we start from existing proposals for an OHS reference architecture and an OHP. We then present a number of scenarios that motivate modifications to these existing proposals. These modifications primarily include adding the notion of an open structure processing layer to the reference architecture and adding a fixed minimal set of guaranteed services to the protocol. We then present our resultant reference architecture and protocol proposals. Our proposals are based on current working group proposals, but incorporate the modifications suggested by our scenarios. Finally, we conclude with some comments on the process we used to derive our proposals, an evaluation of current progress of the OHS Working Group, and suggestions for future directions.

This paper contributes to an ongoing effort on standardizing open hypermedia system architectures and communication interfaces. Open hypermedia systems share the property of being able to provide non-hypermedia applications with hypermedia structuring and navigation capabilities. This support is currently provided in many different ways. To be able to standardize communication interfaces, it is necessary to develop common understanding of the different architectures of existing systems and to develop a common reference architecture for open hypermedia systems. A reference architecture should provide a common language for the design of open hypermedia systems in terms of architectural elements and interfaces. The paper identifies a number of important requirements and characteristics for open hypermedia systems and examines some of the most well known open hypermedia architectures and reference models. The analysis illuminates the commonalties and differences in terminology and architectural elements. The analytical results are used to propose common terminology and a common reference architecture for open hypermedia systems (CoReArc). CoReArc identifies several different architectural elements and communication interfaces for potential interface standardization. Interface standardization may be achieved through a single physical protocol with several suites or topics or through several independent protocols. CoReArc can be used to identify and discuss the different communication interfaces of an open hypermedia system.

Metadata interoperability is a fundamental requirement for access to information within networked knowledge organization systems. The Harmony international digital library project has developed a common underlying data model (the ABC model) to enable the scalable mapping of metadata descriptions across domains and media types. The ABC model provides a set of basic building blocks for metadata modeling and recognizes the importance of 'events' to describe unambiguously metadata for objects with a complex history. To test and evaluate the interoperability capabilities of this model, we applied it to some real multimedia examples and analysed the results of mapping from the ABC model to various different metadata domains using XSLT. This work revealed serious limitations in the ability of XSLT to support flexible dynamic semantic mapping. To overcome this, we developed MetaNet, a metadata term thesaurus which provides the additional semantic knowledge that is non-existent within declarative XML-encoded metadata descriptions. This paper describes MetaNet, its RDF Schema representation and a hybrid mapping approach which combines the structural and syntactic mapping capabilities of XSLT with the semantic knowledge of MetaNet, to enable flexible and dynamic mapping among metadata standards.

We suggest that building "permissive, but robust" digital library systems and services is an attractive alternative to the library and computer science tradition of building "strict, but fragile" systems. Strict, but fragile, systems are efforts to engineer complete systems that ensure desired properties, but which often prove impractical in distributed environments without a central authority to coordinate change. In the permissive, but robust, approach, we permit individual components to change in ways that might, in fact, cause a desired property to fail to persist. However, we engineer components to be robust, so that it is likely that desired properties persist even under a great deal of uncoordinated change. We have applied the permissive, but robust, approach to two related problems of reference in distributed information systems. The first application yields robust hyperlinks, and the second, robust locations. Robust hyperlinks address the familiar issue of providing persistent reference to networked resources, such as Web pages, given changing, uncooperating services. Robust locations concern a somewhat less familiar, but, we suspect, soon-to-be just as big a problem, namely, references to changing sub-document resources. Robust locations, we suggest, provide essential grounding for next-generation web functionality, such as annotations that survive document editing. In both cases, robustness is achieved by providing multiple, independent descriptions across boundaries where change is likely to be uncoordinated. If the different descriptions are property selected, then most uncoordinated changes will be unlikely to cause all the descriptions to fail. Thus, while there is no guarantee that references will remain coherent, a single failure is unlikely to be catastrophic. Instead, the failure of one, even a primary, method will generally allow graceful recovery via other methods.

For the past two years the Massachusetts Institute of Technology (MIT) Libraries and Hewlett-Packard Labs have been collaborating on the development of an open source system called DSpace that functions as a repository for the digital research and educational material produced by members of a research university or organization. Running such an institutionally-based, multidisciplinary repository is increasingly seen as a natural role for the libraries and archives of research and teaching organizations. As their constituents produce increasing amounts of original material in digital formats — much of which is never published by traditional means — the repository becomes vital to protect the significant assets of the institution and its faculty. The first part of this article describes the DSpace system including its functionality and design, and its approach to various problems in digital library and archives design. The second part discusses the implementation of DSpace at MIT, plans for federating the system, and issues of sustainability.

In November 2000, the OMG made public the MDA initiative, a particular variant of a new global trend called MDE (Model Driven Engineering). The basic ideas of MDA are germane to many other approaches such as generative programming, domain specific languages, model-integrated computing, generic model management, software factories, etc. MDA may be defined as the realization of MDE principles around a set of OMG standards like MOF, XMI, OCL, UML, CWM, SPEM, etc. MDE is presently making several promises about the potential benefits that could be reaped from a move from code-centric to model-based practices. When we observe these claims, we may wonder when they may be satisfied: on the short, medium or long term or even never perhaps for some of them. This paper tries to propose a vision of the development of MDE based on some lessons learnt in the past 30 years in the development of object technology. The main message is that a basic principle ("Everything is an object") was most helpful in driving the technology in the direction of simplicity, generality and power of integration. Similarly in MDE, the basic principle that "Everything is a model" has many interesting properties, among others the capacity to generate a realistic research agenda. We postulate here that two core relations (representation and conformance) are associated to this principle, as inheritance and instantiation were associated to the object unification principle in the class-based languages of the 80's. We suggest that this may be most useful in understanding many questions about MDE in general and the MDA approach in particular. We provide some illustrative examples. The personal position taken in this paper would be useful if it could generate a critical debate on the research directions in MDE.

In the proposed data model for XML databases, an XML element is directly represented as a ground (variable-free) XML expression — a generalization of an XML element by incorporation of variables for representation of implicit information and enhancement of its expressive power — while a collection of XML documents as a set of ground expressions, each describing an XML element in the documents. Axioms and relationships among elements in the collection as well as structural and integrity constraints are formalized as XML clauses. An XML database, consisting of: (i) a document collection (or an extensional database), (ii) a set of axioms and relationships (or an intensional database), (iii) a set of integrity constraints, is therefore modeled as an XML declarative description comprising a set of ground XML expressions and XML clauses. Its semantics is a set of ground XML expressions, which are explicitly described by the extensional database or implicitly derived from the database, based on the defined intensional database, and satisfy all the specified set of constraints. Thus, selective and complex queries, formulated as sets of XML clauses, about information satisfying specific criteria and possibly implicit in the database, become expressible and computable. The model thereby serves as an effective and well-founded XML database management framework with succinct representational and operational uniformity, reasoning capabilities as well as complex and deductive query supports.

There are three classical algorithms to compute a finite automaton from a regular expression. The Brzozowski algorithm yields a deterministic automaton, the Glushkov algorithm a nondeterministic one, and the general step by step method generally yields a NFA with ε-transitions. Berry and Sethi have adapted Brzozowski's algorithm to compute the Glushkov automaton of an expression. We describe a variant of the step by step construction which associates standard and trim automata to regular languages. We show that the automaton constructed by the variant and the Glushkov automaton (computed by Berry-Sethi algorithm) are isomorphic.

Based on his many years of experience, a JMEMS editor provides guidelines for authors that will, if followed, greatly reduce the risk of a devastatingly negative result from the review process. The premise is that there are certain things that rightfully anger reviewers, and, once angered, the reviewers become both negative and aggressive in their judgments — hence, the imagery of "the reviewer's axe" and how to avoid it.

User-interface design seeks to improve all human-computer communication and interaction. Increasingly, challenges for the disabled and elderly must be met. Experience gained can help solve fundamental challenges for the general population of users. A recent international conference in Japan, "Universal Design," catalogues both the accomplishments and work to be done in this worldwide arena.

Web 2.0 has become a generic phrase summing up everything that is hot and new about the Internet. However, underneath it lie some fundamental concepts, including the writeable web, increased audience participation, and a move away from traditional 'click and wait' web applications, in which input was delivered on a page by page basis. AJAX (asynchronous JavaScript and XML) is a programming mechanism that has enabled developers to deliver a better experience to web users. However, just as basic JavaScript validation mechanisms did before it, AJAX-based applications may be subject to abuse by intruders who can launch attacks designed to bypass login scripts, for example. Programmers and project managers must come to terms with the tension between a better user experience and the potential for security flaws. One way to resolve them is to use robust coding techniques to protect applications.

The Pathfinder project makes inventive use of relational database technology — originally developed to process data of strictly tabular shape?to construct efficient database — supported XML and XQuery processors. Pathfinder targets database engines that implement a set-oriented mode of query execution: many off-the-shelf traditional database systems make for suitable XQuery runtime environments, but a number of off-beat storage back-ends fit that bill as well. While Pathfinder has been developed with a close eye on the XQuery semantics, some of the techniques that we will review here will be generally useful to evaluate XQuery-style iterative languages on database back-ends.

In this paper, we describe the TIMBER XML database system implemented at University of Michigan. TIMBER was one of the first native XML database systems, designed from the ground up to store and query semi-structured data. A distinctive principle of TIMBER is its algebraic underpinning. Central contributions of the TIMBER project include: (1) tree algebras that capture the structural nature of XML queries; (2) the stack-based family of algorithms to evaluate structural joins; (3) new rule-based query optimization techniques that take care of the heterogeneous nature of the intermediate results and take the schema information into consideration; (4) cost-based query optimization techniques and summary structures for result cardinality estimation; and (5) a family of structural indices for more efficient query evaluation. In this paper, we describe not only the architecture of TIMBER, its storage model, and engineering choices we made, but also present in hindsight, our retrospective on what went well and not so well with our design and engineering choices.

In this paper, we describe XQuery compilation and rewrite optimization in DB2 pureXML, a hybrid relational and XML database management system. DB2 pureXML has been designed to scale to large collections of XML data. In such a system, effective filtering of XML documents and efficient execution of XML navigation are vital for high throughput. Hence the focus of rewrite optimization is to consolidate navigation constructs as much as possible and to pushdown comparison predicates and navigation constructs into data access to enable index usage. In this paper, we describe the new rewrite transformations we have implemented specifically for XQuery and its navigational constructs. We also briefly discuss how some of the existing rewrite transformations developed for the SQL engine are extended and adapted for XQuery.

Since the birth of XML, the processing of XML query languages like XQuery/XQueryP has been widely researched in the academic and industrial communities. Most of the approaches consider XQuery as a declarative query language similar to SQL, for which the iterator-based (stream-based), lazy evaluation processing strategy can be applied. The processing is combined with XML indexing, materialized view, XML view query rewrite over source data. An alternative approach views XQuery as a procedural programming language associated with eager, step-based evaluation, where each expression is fully evaluated by the end of the corresponding expression execution step. Usually, this approach uses a virtual machine running byte-code for compiled programs. In this paper, we share our experience of building a unified XQuery engine for the Oracle XML DB integrating both approaches. The key contribution of our approach is that the unified XQuery processor integrates both declarative and imperative XQuery/XQueryP processing paradigms. Furthermore, the processor is designed with a clean separation between the logical XML data model and the physical representation so that it can be optimized with various physical XML storages and data index and view models. We also discuss the challenges in our approach and our overall vision of the evolution of XQuery/XQueryP processors.

Increasingly, companies recognize that most of their important information does not exist in relational stores but in documents. For a long time, textual information has been relatively inaccessible and unusable. Database applications allow relational data to be used and re-used; the architecture of relational database systems allow such applications to function even in the face of large amounts of data. XML and XQuery now allow the creation of a new kind of application that unlocks content in a similar way: a content application. In this paper, we examine the technologies that enable content applications to operate at scale in the context of MarkLogic Server.

In this paper, we describe our experiences in building and evolving an XQuery engine with a focus on data and service federation use cases. The engine that we discuss is a core component of the BEA AquaLogic Data Services Platform product (recently re-released under the name Oracle Data Service Integrator). This XQuery engine was designed to provide efficient query and update capabilities over various classes of enterprise data sources, serving as the data access layer in a service-oriented architecture (SOA). The goal of this paper is to give an architectural overview of the engine, discussing some of the key implementation techniques that were employed as well as several XQuery language extensions that were introduced to address common data and service integration problems and challenges.

Software infrastructures and applications more and more must deal with data available in a variety of different storage engines, accessible through a multitude of protocols and interfaces; and it is common that the size of the data involved requires streaming-based processing. This article shows how XQuery can leverage the XML Data Model to abstract the data physical details and to offer optimized processing allowing the development of highly scalable and performant data integration solutions.

This paper describes the internal features of the Saxon XQuery processor that make the most significant contribution to its speed of execution. For each of the features, an attempt is made to quantify the contribution, in most cases by comparing performance achieved when the feature is enabled or disabled.

We have developed YFilter, an XML filtering system that provides fast, on-the-fly matching of XML-encoded data to large numbers of query specifications containing constraints on both structure and content. YFilter encodes path expressions using a novel NFA-based approach that enables highly-efficient, shared processing for large numbers of XPath expressions. In this paper, we provide a brief technical overview of YFilter, focusing on the NFA model, its implementation, and its performance characteristics.

A critical challenge facing the pervasive computing research community is the need to manage complex interactions among numerous interconnected computers and devices. In such a pervasive space, a given application's functionalities are partitioned and distributed across several computing devices that are spontaneously discovered and used. In recent years, researchers have devoted much attention to universal interactions with diverse devices in richly networked settings. We can categorize the numerous approaches explored into two groups: universal user interface languages and user interface remoting. We review recent noteworthy efforts for universal interactions using these two approaches. Such efforts aim to raise interoperability in interactive smart spaces by standardizing user interface languages or communication protocols.

Learn about principles of opportunistic design through an interview study of 14 professional and hobbyist "mashers" from three design disciplines: Web 2.0, hardware, and ubiquitous computing.

We investigated whether students liked and learned more from PowerPoint presentations than from overhead transparencies. Students were exposed to lectures supported by transparencies and two different types of PowerPoint presentations. At the end of the semester, students preferred PowerPoint presentations but this preference was not found on ratings taken immediately after the lectures. Students performed worse on quizzes when PowerPoint presentations included non-text items such as pictures and sound effects. A second study further examined these findings. In this study participants were shown PowerPoint slides that contained only text, contained text and a relevant picture, and contained text with a picture that was not relevant. Students performed worse on recall and recognition tasks and had greater dislike for slides with pictures that were not relevant. We conclude that PowerPoint can be beneficial, but material that is not pertinent to the presentation can be harmful to students' learning.

Many web pages are rich in geographic information and primarily relevant to geographically limited communities. However, existing IR systems only recently began to offer local services and largely ignore geo-spatial information. This paper presents our work on automatically identifying the geographical scope of web documents, which provides the means to develop retrieval tools that take the geographical context into consideration. Our approach makes extensive use of an ontology of geographical concepts, and includes a system architecture for extracting geographic information from large collections of web documents. The proposed method involves recognising geographical references over the documents and assigning geographical scopes through a graph ranking algorithm. Initial evaluation results are encouraging, indicating the viability of this approach.

Geographic Information Systems (GIS) are moving from isolated, standalone, monolithic, proprietary systems working in a client-server architecture to smaller web-based applications and components offering specific geo-processing functionality and transparently exchanging data among them. Interoperability is at the core of this new web services model. Compliance with Open Specifications (OS) enables interoperability. Web-GIS software's high costs, complexity and special requirements have prevented many organizations from deploying their data and geo-processing capabilities over the World Wide Web. There are no-cost Open Source Software (OSS) alternatives to proprietary software for operating systems, web servers, and Relational Database Management Systems. We tested the potential of the combined use of OS and OSS to create web-based spatial information solutions. We present in detail the steps taken in creating a prototype system to support land use planning in Mexico with web-based geo-processing capabilities currently not present in commercial web-GIS products. We show that the process is straightforward and accessible to a broad audience of geographic information scientists and developers. We conclude that OS and OSS allow the development of web-based spatial information solutions that are low-cost, simple to implement, compatible with existing information technology infrastructure, and have the potential of interoperating with other systems and applications in the future.

Two kinds of contemporary developments in cryptography are examined. Widening applications of teleprocessing have given rise to a need for new types of cryptographic systems, which minimize the need for secure key distribution channels and supply the equivalent of a written signature. This paper suggests ways to solve these currently open problems. It also discusses how the theories of communication and computation are beginning to provide the tools to solve cryptographic problems of long standing.

An entity relationship oriented model, that includes the notion of class, together with different types of assertions on classes, is presented. The assertions are used to model IS-A and disjointness relations both between entities and between relationships, part-of relations between entities and relationships, mandatory participation of an entity in a relationship, and interdependencies between the projections of relationships. The semantics of the model are defined in terms of first-order logic, and a sound and complete inference algorithm for such a model is presented. The algorithm is shown to have polynomial time complexity in the case where interdependencies on the projections of relationships are not taken into account. It is suggested that the model and the associated inference capabilities provide a suitable formal basis for designing an effective environment supporting conceptual modeling.

As XML data becomes more and more prevalent and as larger quantities of data find their way into XML documents, the need for quality XML data organization will only increase. One standard way of structuring data well is to reduce and, if possible, eliminate redundancy, while at the same time making the storage structures as compact as possible. In this paper, we present a methodology to generate XML storage structures where conforming XML documents are redundancy-free, and for most practical cases, are also fully compact. Our methodology assumes the input is a conceptual-model hypergraph. For the special case that every edge in the hypergraph is binary, we present a simple algorithm, guaranteed to always generate redundancy-free storage structures. We show, however, that generating a minimum number of redundancy-free storage structures is NP-hard. We therefore provide heuristics to guide the process and observe that these heuristics result in satisfactory solutions, which are often optimal. We then present a general algorithm for n-ary edges and show that it generates redundancy-free storage structures. The general algorithm must overcome several problems that do not arise in the special case.

Research and development on the technologies of locating the mobile (wireless) phone caller have been rapidly gaining momentum around the world. Once these technologies are mature enough to be deployed, they will have significant impact on automotive telematics and modern public transit systems. In this paper, we discuss why locating mobile phones becomes a hot topic among telecommunications giants, what technologies are being studied and standardized, when we are going to see the actual deployment, and what services they may provide? We then consider its potential impact on future intelligent transportation systems, including telematics and public transit systems. Many of us have already recognized how important a role the communications systems play in modern transportation. In the near future, if every mobile phone is able to determine its location, advances in our current transportation systems become inevitable

Finding the location of the mobile phone is one of the important features of the 3G mobile communication system. Many valuable location-based services can be enabled by this new feature. Telecommunication managers and engineers are often puzzled by location terminologies and techniques as well as how to implement them, since location systems are not natural evolution from past generations of telecommunication systems. In this paper, we discuss briefly why locating mobile phone becomes a hot topic and what technologies are being studied. We then describe and clarify the latest standards issues surrounding the positioning methods specified for 3G systems. These include cell-ID-based, assisted GPS, and TDOA-based methods, such as OTDOA, E-OTD, and A-FLT

The main difficulties in designing collaborative-learning applications are understanding which interactions between learners and teachers are the appropriate ones and then building software that takes such dynamics into account. Some researchers address this challenge by defining reusable components for specific learning tasks. The problems are that developers impose their particular solution, adapting components to requirement changes requires much effort, developers might lack the expertise to identify the appropriate group dynamics, and the resulting software might be used in unexpected ways. An approach based on an interaction model lets designers and educational experts specify the interactions in a learning activity. They can then define a set of reusable interaction components. The resulting flexible model is the basis for a flexible architecture that lets you create, extend, reuse, and compose diverse educational software products.

Asynchronous processing models can be highly efficient but are not without challenges. If the real world writes the best stories, then maybe we can learn something from Starbucks about designing successful asynchronous messaging solutions.

A computer system which stores, retrieves and manipulates information about some portion of the real world can be viewed as a model of that domain of discourse. There has been considerable research recently on languages which allow one to capture more of the semantics of the real world in these computerized Information Systems — research which has variously been labelled as Semantic Data Modeling, Semantic Modeling or Conceptual Modeling. This review paper presents a list of the features which appear to distinguish these languages from those traditionally used to describe and develop database-intensive applications, and considers the motivation for these features as well as the potential advantages to be gained through their use. The paper, which is intended for those familiar with current data processing practices, also compares in greater detail four programming languages which incorporate semantic modeling facilities, and discusses some of the methodologies and tools for Information System development based on these languages.

The Object Management Group's model driven architecture defines a system development approach that formally separates system specification from platform implementations — in platform-independent models and platform-specific models, respectively. According to MDA, software development involves a sequence of model mappings that transform an initial PIM to a final PSM that is precise enough for direct translation into an executable program. A mapping is a set of rules and techniques for translating one model into another. When the starting and final models are expressed in the same formalism, the mapping is said to be intralanguage; otherwise, it is interlanguage. We focus here on interlanguage mapping, showing the central role of formalism extension mechanisms in managing the abstraction-level gap between languages as well as the platform-level details of specific implementations.

Services based on the representational state transfer (REST) paradigm, a lightweight implementation of a service-oriented architecture, have found even greater success than their heavyweight siblings, which are based on the Web Services Description Language (WSDL) and SOAP. By using XML-based messaging, RESTful services can bring together discrete data from different services to create meaningful data sets; mashups such as these are extremely popular today.

The Stream Control Transmission Protocol (SCTP) is a general-purpose IETF transport protocol with kernel implementations on various platforms. Similar to TCP, SCTP provides a connection-oriented, reliable, congestion and flow-controlled layer 4 channel. Unlike both TCP and UDP, however, SCTP offers new delivery options that better match diverse applications' needs.

A new form of personal identity is emerging on the Web. Decentralized identification protocols depart from traditional distributed authentication approaches developed for the Internet. What distinguishes this new approach is its use of URIs as the underlying identifier.

This paper provides some abstractions and roadmaps for interpreting data-intensive Web applications. This class of applications is characterized by the underlying existence of large data sets, organized within a repository or database, and therefore must obey some typical patterns and rules for the effective management of information. The purpose of this paper is to explain such patterns and rules in terms of WebML, a formal Web modeling language, for specifying the content structure of the Web application and the organization and presentation of such content in a hypertext. In particular, the paper shows that data-intensive Web sites can be abstracted as complex arrangements of elementary structures, called skeletons, which are pairs of structural diagrams (describing data organizations) and site view diagrams (describing navigational patterns). The essence of the proposed method is the classification of the role that concepts may play within the Web application information content, so that it can be abstracted and reduced to few, fundamental entities and relationships, organized according to an E/R diagram. Such a classification then feeds the identification of WebML skeletons.

Traditional approaches to software development ? the ones embodied in CASE tools and modeling frameworks — are appropriate for building individual software components, but they are not designed to face the challenges of open environments. Service-oriented computing provides a way to create a new architecture that reflects components' trends toward autonomy and heterogeneity.

Early syndication and publishing protocols faced various problems related to interoperability, scalability, and extensibility. The Atom format and protocol builds on earlier efforts to establish an open, extensible, interoperable, and clearly specified framework for Web-logging applications. Atom has already been deployed on a wide variety of platforms. By closely examining previous syndication formats and protocols, the AtomPub working group has been able to "pave the footpaths", and design a standard built around well-known and proven usage patterns.

Semantic Web technologies have been around for a while. However, such technologies have had little impact on the development of real-world Web applications to date. With linked data, this situation has changed dramatically in the past few months. This article shows how linked data sets can be exploited to build rich Web applications with little effort.

Web services are frequently described as the latest incarnation of distributed object technology. This misconception, perpetuated by people from both industry and academia, seriously limits broader acceptance of the true Web services architecture. Although the architects of many distributed and Internet systems have been vocal about the differences between Web services and distributed objects, dispelling the myth that they are closely related appears difficult. Many believe that Web services is a distributed systems technology that relies on some form of distributed object technology. Unfortunately, this is not the only common misconception about Web services. We seek to clarify several widely held beliefs about the technology that are partially or completely wrong. Within the distributed technology world, it is probably more appropriate to associate Web services with messaging technologies because they share a common architectural view, although they address different application types. Web services technology will have a dramatic enabling effect on worldwide interoperable distributed computing once everyone recognizes that Web services are about interoperable document-centric computing, not distributed objects.

XML technologies are very popular, and one of the most important reasons for this is the availability of tools and technologies for working with XML, eliminating the need to build XML processing from scratch. However, XML technologies are built on top of inherent (and not always well-defined) information models, and this may cause problems because (1) the information models of some tools may not support the required "view" of XML, or (2) there is no appropriate data model to work with the information model in question. In this article, we approach this question from the systematic side, and describe the most prominent XML technologies with regard to their information and data models.

Compared to approaches such as Web services and the Web Services Description Language (WSDL), which promote specialization for each service interface, the uniform-interface constraint reduces client-server coupling and helps minimize gratuitous differences in interface and method semantics across disparate resources. REST isn't a silver bullet, but its flexibility and relative simplicity make it highly applicable not only to Web-scale systems but also to a wide variety of enterprise integration problems. The representational state transfer (REST) architectural style, on the other hand, makes very specific and highly useful trade-offs meticulously chosen to enhance the scalability, extensibility, manageability, and maintainability of distributed systems and applications.

Representational State Transfer (REST) architectural style proponents describe it as being easy, but this in no way implies that REST is trivial or simplistic, nor does it mean that RESTful systems lack sophistication. The author covers the primary areas that developers must continually consider as they design and build Web services. Tools can certainly provide reminders about these areas and help to track progress, but ultimately, developers must understand the underlying technical issues to be able to make suitable design and implementation choices.

Despite the fact that many successful distributed systems have been built using remote procedure calls, we've also known for a while that RPC is imperfect, even fundamentally flawed. Lately, however, it seems to be taking even more heat than usual, mainly because of continuing advances in Web services and XML-based messaging.

As I discussed in my previous column, each different style of middleware promotes one or more interaction models that determine how applications based on that middleware communicate and work with each other. It is difficult to say what the best interaction models would be for Web services, mainly because the World Wide Web Consortium (W3C) is still developing the architecture. The author considers the use of remote procedure calls, Web services and messaging and interface complexity.

Developers risk negative side effects when they attempt to make Web services interfaces extensible without understanding the context in which various mechanisms are applied. Given the overuse and misapplication of the HTML example,developers often litter their interfaces with XML Schema wildcards. This increases complexity and results in ambiguous interface definitions. A more appropriate versioning strategy for Web services development can help developers avoid these problems.

As the use of Web services grows, organizations are increasingly choosing the Business Process Execution Language for modeling business processes within the Web services architecture. In addition to orchestrating organizations' Web services, BPEL's strengths include asynchronous message handling, reliability, and recovery. By developing Web services with BPEL in mind, organizations can implement aspects of the service-oriented architecture that might previously have been difficult to achieve.

If the next Presidential administration really wants to embrace the potential of Internet-enabled government transparency, it should follow a counter-intuitive but ultimately compelling strategy: reduce the federal role in presenting important government information to citizens. Today, government bodies consider their own websites to be a higher priority than technical infrastructures that open up their data for others to use. We argue that this understanding is a mistake. It would be preferable for government to understand providing reusable data, rather than providing websites, as the core of its online publishing responsibility. Rather than struggling, as it currently does, to design sites that meet each end-user need, we argue that the executive branch should focus on creating a simple, reliable and publicly accessible infrastructure that exposes the underlying data. Private actors, either nonprofit or commercial, are better suited to deliver government information to citizens and can constantly create and reshape the tools individuals use to find and leverage public data. The best way to ensure that the government allows private parties to compete on equal terms in the provision of government data is to require that federal websites themselves use the same open systems for accessing the underlying data as they make available to the public at large.

Mobile devices such as personal digital assistants (PDAs) and mobile phones are in widespread use already today and converging to mobile smart phones. They enable users to access a wide range of services and information without guidance through their actual demands. Especially during mass events like the Olympic Games 2008 in Beijing — which was initially the context of our work — a large service space is expected to support all mobile visitors, being athletes, journalists, or spectators. Current approaches tackling such problems are location based, meaning that a user's location is central to service provision, and even context-aware, meaning that, beyond location, characteristics of a user's environment are taken into account. Such information obviously helps to deliver relevant information at the right time to the mobile users. Going one step further, a situation-aware system abstracts from the context dimensions by translating specific contexts into logical situations. Knowing the situation end users are in allows the system to better identify the information to be delivered to them and to choose the appropriate services with regard to their scope, which is referred to as service roaming. Even though many context frameworks have been introduced in the past few years, what is usually missing is the notion of characteristic features of contexts that are invariant during certain time intervals. This paper presents these concepts in the context of a platform development, namely FLAME2008, which is able to support its mobile users with personalized situation-aware services in push and pull mode.

The tremendous increase in the use of cellular phones, GPS-like devices, and RFIDs results in highly dynamic environments where objects as well as queries are continuously moving. In this paper, we present a continuous query processor designed specifically for highly dynamic environments (e.g., location-aware environments). We implemented the proposed continuous query processor inside the PLACE server (Pervasive Location-Aware Computing Environments); a scalable location-aware database server developed at Purdue University. The PLACE server extends data streaming management systems to support location-aware environments. These environments are characterized by the wide variety of continuous spatio-temporal queries and the unbounded spatio-temporal streams. The proposed continuous query processor includes: (1) New incremental spatio-temporal operators to support a wide variety of continuous spatio-temporal queries, (2) Extended semantics of sliding window queries to deal with spatial sliding windows as well as temporal sliding windows, and (3) A shared-execution framework for scalable execution of a set of concurrent continuous spatio-temporal queries. Experimental evaluation shows promising performance of the continuous query processor of the PLACE server.

Workflow management and service composition technologies have been around for over twenty years now (or more, depending on who you ask and how you define them). The objective of these technologies is to automate process execution across people and systems. These technologies generated an incredible hype both in the academia and in the industry, at least in the software development industry. Hundreds of process and service composition models have been defined, thousands of papers have been written on the topic, and dozens of commercial workflow/service composition systems have been developed. With all this large effort, one would imagine that such technology is in widespread use and that, if not, the key problems have been identified and that is what generates so much effort from the research community. I believe that this is not the case.

Today's wiki engines are not interoperable. This is an unfortunate consequence of the lack of rigorously specified standards. This technical report presents a complete and validated EBNF-based grammar for Wiki Creole, a community standard for wiki markup. Wiki Creole is also the only standard currently available. Wiki Creole is being specified using prose, leading to inconsistencies and ambiguities. Our grammar uncovered those ambiguities which we fed back into the specification process. The Wiki Creole grammar presented in this report makes the creation of Wiki Creole parsers simple using parser generators, ANTLR in our case. Using a precise specification of wiki markup lets us decouple wiki editors from wiki storage from further wiki processing tools. Based on this decoupling layer we expect innovation on these different parts to proceed independently and at a faster pace than before.

Wikis have become an important application on the web and in the enterprise, yet there are no interoperability standards between different wiki engines. We present the first complete XML representation format of Wiki Creole 1.0. Wiki Creole is a community standard for wiki markup, the language used to write wiki pages. This report presents the complete XML representation format using a validating XML schema. In addition we present XSLT definitions for transforming the XML representations to XHTML on the one hand and for transforming the XML representations to Wiki Creole markup on the other hand. Our work shows how using XML technologies we can make wiki interchange, wiki upgrading, and wiki conversion independent from a specific wiki engine implementation.

One relatively unexplored question about the Internet's physical structure concerns the geographical location of its components: routers, links, and autonomous systems (ASes). We study this question using two large inventories of Internet routers and links, collected by different methods and about two years apart. We first map each router to its geographical location using two different state-of-the-art tools. We then study the relationship between router location and population density; between geographic distance and link density; and between the size and geographic extent of ASes. Our findings are consistent across the two datasets and both mapping methods. First, as expected, router density per person varies widely over different economic regions; however, in economically homogeneous regions, router density shows a strong superlinear relationship to population density. Second, the probability that two routers are directly connected is strongly dependent on distance; our data is consistent with a model in which a majority (up to 75%-95%) of link formation is based on geographical distance (as in the Waxman (1988) topology generation method). Finally, we find that ASes show high variability in geographic size, which is correlated with other measures of AS size (degree and number of interfaces). Among small to medium ASes, ASes show wide variability in their geographic dispersal; however, all ASes exceeding a certain threshold in size are maximally dispersed geographically. These findings have many implications for the next generation of topology generators, which we envisage as producing router-level graphs annotated with attributes such as link latencies, AS identifiers, and geographical locations.

This article uses data from the social bookmarking site del.icio.us to empirically examine the dynamics of collaborative tagging systems and to study how coherent categorization schemes emerge from unsupervised tagging by individual users. First, we study the formation of stable distributions in tagging systems, seen as an implicit form of "consensus" reached by the users of the system around the tags that best describe a resource. We show that final tag frequencies for most resources converge to power law distributions and we propose an empirical method to examine the dynamics of the convergence process, based on the Kullback-Leibler divergence measure. The convergence analysis is performed for both the most utilized tags at the top of tag distributions and the so-called long tail. Second, we study the information structures that emerge from collaborative tagging, namely tag correlation (or folksonomy) graphs. We show how community-based network techniques can be used to extract simple tag vocabularies from the tag correlation graphs by partitioning them into subsets of related tags. Furthermore, we also show, for a specialized domain, that shared vocabularies produced by collaborative tagging are richer than the vocabularies which can be extracted from large-scale query logs provided by a major search engine. Although the empirical analysis presented in this article is based on a set of tagging data obtained from del.icio.us, the methods developed are general, and the conclusions should be applicable across other websites that employ tagging.

We describe an approach for extracting semantics for tags, unstructured text-labels assigned to resources on the Web, based on each tag's usage patterns. In particular, we focus on the problem of extracting place semantics for tags that are assigned to photos on Flickr, a popular-photo sharing Web site that supports location (latitude/longitude) metadata for photos. We propose the adaptation of two baseline methods, inspired by well-known burst-analysis techniques, for the task; we also describe two novel methods, TagMaps and scale-structure identification. We evaluate the methods on a subset of Flickr data. We show that our scale-structure identification method outperforms existing techniques and that a hybrid approach generates further improvements (achieving 85% precision at 81% recall). The approach and methods described in this work can be used in other domains such as geo-annotated Web pages, where text terms can be extracted and associated with usage patterns.

We discuss the definition of keys for XML documents, paying particular attention to the concept of a relative key, which is commonly used in hierarchically structured documents and scientific databases.

Integrity constraints are an essential part of modern schema definition languages. They are useful for semantic specification, update consistency control, query optimization, etc. In this paper, we propose UCM, a model of integrity constraints for XML that is both simple and expressive. Because it relies on a single notion of keys and foreign keys, the UCM model is easy to use and makes formal reasoning possible. Because it relies on a powerful type system, the UCM model is expressive, capturing in a single framework the constraints found in relational databases, object-oriented schemas and XML document type definitions. We study the problem of consistency of UCM constraints, the interaction between constraints and subtyping, and algorithms for implementing these constraints.

Annotea is a Web-based shared annotation system based on a general-purpose open resource description framework (RDF) infrastructure, where annotations are modeled as a class of metadata. Annotations are viewed as statements made by an author about a Web document. Annotations are external to the documents and can be stored in one or more annotation servers. One of the goals of this project has been to re-use as much existing W3C technology as possible. We have reached it mostly by combining RDF with XPointer, XLink, and HTTP. We have also implemented an instance of our system using the Amaya editor/browser and a generic RDF database, accessible through an Apache HTTP server. In this implementation, the merging of annotations with documents takes place within the client. The paper presents the overall design of Annotea and describes some of the issues we have faced and how we have solved them.

We describe an Extensible Markup Language (XML)-based methodology for Web data extraction that extends beyond simple "screen scraping". An ideal data extraction process can digest target Web databases that are visible only as Hypertext Markup Language (HTML) pages, and create a local replica of those databases as a result. What is needed is more than a Web crawler and set of Web site wrappers. A comprehensive data extraction process must deal with such obstacles as session identifiers, HTML forms, client-side JavaScript, incompatible datasets and vocabularies, and missing and conflicting data. Proper data extraction also requires solid data validation and error recovery to handle data extraction failures. Our ANDES software framework helps solve these problems and provides a platform for building a production-quality Web data extraction process. Key aspects of ANDES are that it uses XML technologies for data extraction, including Extensible HTML and Extensible Stylesheet Language Transformations, and provides access to the "deep Web".

A data model, called the entity-relationship model, is proposed. This model incorporates some of the important semantic information about the real world. A special diagrammatic technique is introduced as a tool for database design. An example of database design and description using the model and the diagrammatic technique is given. Some implications for data integrity, information retrieval, and data manipulation are discussed. The entity-relationship model can be used as a basis for unification of different views of data: the network model, the relational model, and the entity set model. Semantic ambiguities in these models are analyzed. Possible ways to derive their views of data from the entity-relationship model are presented.

A new normal form for relational databases, called domain-key normal form (DK/NF), is defined. Also, formal definitions of insertion anomaly and deletion anomaly are presented. It is shown that a schema is in DK/NF if and only if it has no insertion or deletion anomalies. Unlike previously defined normal forms, DK/NF is not defined in terms of traditional dependencies (functional, multivalued, or join). Instead, it is defined in terms of the more primitive concepts of domain and key, along with the general concept of a "constraint." We also consider how the definitions of traditional normal forms might be modified by taking into consideration, for the first time, the combinatorial consequences of bounded domain sizes. It is shown that after this modification, these traditional normal forms are all implied by DK/NF. In particular, if all domains are infinite, then these traditional normal forms are all implied by DK/NF.

This article takes a first step towards the design and normalization theory for XML documents. We show that, like relational databases, XML documents may contain redundant information, and may be prone to update anomalies. Furthermore, such problems are caused by certain functional dependencies among paths in the document. Our goal is to find away of converting an arbitrary DTD into a well-designed one, that avoids these problems. We first introduce the concept of a functional dependency for XML, and define its semantics via a relational representation of XML. We then define an XML normal form, XNF, that avoids update anomalies and redundancies. We study its properties, and show that XNF generalizes BCNF; we also discuss the relationship between XNF and normal forms for nested relations. Finally, we present a lossless algorithm for converting any DTD into one in XNF.

Although the need for formalisation of modelling techniques is generally recognised, not much literature is devoted to the actual process involved. This is comparable to the situation in mathematics where focus is on proofs but not on the process of proving. This paper tries to accommodate for this lacuna and provides essential principles for the process of formalisation in the context of modelling techniques as well as a number of small but realistic formalisation case studies.

As ontology development becomes a more ubiquitous and collaborative process, ontology versioning and evolution becomes an important area of ontology research. The many similarities between database-schema evolution and ontology evolution will allow us to build on the extensive research in schema evolution. However, there are also important differences between database schemas and ontologies. The differences stem from different usage paradigms, the presence of explicit semantics, and different knowledge models. A lot of problems that existed only in theory in database research come to the forefront as practical problems in ontology evolution. These differences have important implications for the development of ontology evolution frameworks: The traditional distinction between versioning and evolution is not applicable to ontologies. There are several dimensions along which compatibility between versions must be considered. The set of change operations for ontologies is difference. We must develop automatic techniques for finding similarities and differences between versions.

An enhanced version of the Entity-Relationship (ER) data model called the Entity-Category-Relationship (ECR) data model is presented. The principal extension is the introduction of the concept of a category. Categories permit the grouping of entities from different entity types according to the roles they play in a relationship, as well as the representation of ISA and generalization hierarchies. The structures of the ECR data model are defined, and a graphic representation technique for their display is presented. Language operations to define and use an ECR database are defined. Two realistic examples of the use of the ECR model for database design are demonstrated. The examples show how ECR structures can be directly mapped into relational and network structures. The definition of derived relationships on an ECR database gives the power to phrase higher order recursive queries in a first order query language.

This paper presents the conceptual modelling parts of a methodology for the design of large-scale data-intensive web information systems (WISs) that is based on an abstract abstraction layer model (ALM). It concentrates on the two most important layers in this model: a business layer and a conceptual layer. The major activities on the business layer deal with user profiling and storyboarding, which addresses the design of an underlying application story. The core of such a story can be expressed by a directed multi-graph, in which the vertices represent scenes and the edges actions by the users including navigation. This leads to story algebras which can then be used to personalise the WIS to the needs of a user with a particular profile. The major activities on the conceptual layer address the support of scenes by modelling media types, which combine links to databases via extended views with the generation of navigation structures, operations supporting the activities in the storyboard, hierarchical presentations, and adaptivity to users, end-devices and channels.

Three different interfaces were used to browse a large (1296 items) table of contents. A fully expanded stable interface, expand/contract interface, and multipane interface were studied in a between-groups experiment with 41 novice participants. Nine timed fact retrieval tasks were performed; each task is analyzed and discussed separately. We found that both the expand/contract and multipane interfaces produced significantly faster times than the stable interface for many tasks using this large hierarchy; other advantages of the expand/contract and multipane interfaces over the stable interface are discussed. The animation characteristics of the expand/contract interface appear to play a major role. Refinements to the multipane and expand/contract interfaces are suggested. A predictive model for measuring navigation effort of each interface is presented.

The Extensible Markup Language (XML) is fast emerging as the dominant standard for describing and interchanging data among various systems and databases on the Internet. It offers the Document Type Definition (DTD) as a formalism for defining the syntax and structure of XML documents. The XML Schema definition language, as a replacement for the DTD, provides more rich facilities for defining and constraining the content of XML documents. However, it does not concentrate on the semantics that underlies these documents, representing a logical data model rather than a conceptual model. To enable efficient business application development in large-scale electronic commerce environments, it is necessary to describe and model real-world data semantics and their complex interrelationships. In this article, we describe a design methodology for XML documents. The aim is to enforce XML conceptual modeling power and bridge the gap between software development and XML document structures. The proposed methodology is comprised of two design levels: the semantic level and the schema level. The first level is based on a semantic network, which provides semantic modeling of XML through four major components: a set of atomic and complex nodes, representing real-world objects; a set of directed edges, representing semantic relationships between the objects; a set of labels denoting different types of semantic relationships, including aggregation, generalization, association, and of-property relationships; and finally a set of constraints defined over nodes and edges to constrain semantic relationships and object domains. The other level of the proposed methodology is concerned with detailed XML schema design, including element/attribute declarations and simple/complex type definitions. The mapping between the two design levels is proposed to transform the XML semantic model into the XML Schema, based on which XML documents can be systematically created, managed, and validated.

XSL Transformations (XSLT) is a programming language for defining transformations among XML languages. The structure of these languages is formally described by schemas, for example using DTD or XML Schema, which allows individual documents to be validated. However, existing XSLT tools offer no static guarantees that, under the assumption that the input is valid relative to the input schema, the output of the transformation is valid relative to the output schema. We present a validation technique for XSLT based on the XML graph formalism introduced in the static analysis of JWIG Web services and XACT XML transformations. Being able to provide static guarantees, we can detect a large class of errors in an XSLT stylesheet at the time it is written instead of later when it has been deployed, and thereby provide benefits similar to those of static type checkers for modern programming languages. Our analysis takes a pragmatic approach that focuses its precision on the essential language features but still handles the entire XSLT language. We evaluate the analysis precision on a range of real stylesheets and demonstrate how it may be useful in practice.

We propose regular expression types as a foundation for statically typed XML processing languages. Regular expression types, like most schema languages for XML, introduce regular expression notations such as repetition (*), alternation (|), etc., to describe XML documents. The novelty of our type system is a semantic presentation of subtyping, as inclusion between the sets of documents denoted by two types. We give several examples illustrating the usefulness of this form of subtyping in XML processing. The decision problem for the subtype relation reduces to the inclusion problem between tree automata, which is known to be EXPTIME-complete. To avoid this high complexity in typical cases, we develop a practical algorithm that, unlike classical algorithms based on determinization of tree automata, checks the inclusion relation by a top-down traversal of the original type expressions. The main advantage of this algorithm is that it can exploit the property that type expressions being compared often share portions of their representations. Our algorithm is a variant of Aiken and Murphy's set-inclusion constraint solver, to which are added several new implementation techniques, correctness proofs, and preliminary performance measurements on some small programs in the domain of typed XML processing.

The increasing importance being placed on software measurement has led to an increased amount of research developing new software measures. Given the importance of object-oriented development techniques, one specific area where this has occurred is coupling measurement in object-oriented systems. However, despite a very interesting and rich body of work, there is little understanding of the motivation and empirical hypotheses behind many of these new measures. It is often difficult to determine how such measures relate to one another and for which application they can be used. As a consequence, it is very difficult for practitioners and researchers to obtain a clear picture of the state-of-the-art in order to select or define measures for object-oriented systems. This situation is addressed and clarified through several different activities. First, a standardized terminology and formalism for expressing measures is provided which ensures that all measures using it are expressed in a fully consistent and operational manner. Second, to provide a structured synthesis, a review of the existing frameworks and measures for coupling measurement in object-oriented systems takes place. Third, a unified framework, based on the issues discovered in the review, is provided and all existing measures are then classified according to this framework. This paper contributes to an increased understanding of the state-of-the-art: A mechanism is provided for comparing measures and their potential use, integrating existing measures which examine the same concepts in different ways, and facilitating more rigorous decision making regarding the definition of new measures and the selection of existing measures for a specific goal of measurement. In addition, our review of the state-of-the-art highlights that many measures are not defined in a fully operational form, and relatively few of them are based on explicit empirical models, as recommended by measurement theory.

The World Wide Web has succeeded in large part because its software architecture has been designed to meet the needs of an Internet-scale distributed hypermedia application. The modern Web architecture emphasizes scalability of component interactions, generality of interfaces, independent deployment of components, and intermediary components to reduce interaction latency, enforce security, and encapsulate legacy systems. In this article we introduce the Representational State Transfer (REST) architectural style, developed as an abstract model of the Web architecture and used to guide our redesign and definition of the Hypertext Transfer Protocol and Uniform Resource Identifiers. We describe the software engineering principles guiding REST and the interaction constraints chosen to retain those principles, contrasting them to the constraints of other architectural styles. We then compare the abstract model to the currently deployed Web architecture in order to elicit mismatches between the existing protocols and the applications they are intended to support.

Identity is that property of an object which distinguishes each object from all others. Identity has been investigated almost independently in general-purpose programming languages and database languages. Its importance is growing as these two environments evolve and merge. We describe a continuum between weak and strong support of identity, and argue for the incorporation of the strong notion of identity at the conceptual level in languages for general purpose programming, database systems and their hybrids. We define a data model that can directly describe complex objects, and show that identity can easily be incorporated in it. Finally, we compare different implementation schemes for identity and argue that a surrogate-based implementation scheme is needed to support the strong notion of identity.

The motivation behind the work in very-high-level languages is to ease the programming task by providing the programmer with a language containing primitives or abstractions suitable to his problem area. The programmer is then able to spend his effort in the right place; he concentrates on solving his problem, and the resulting program will be more reliable as a result. Clearly, this is a worthwhile goal. Unfortunately, it is very difficult for a designer to select in advance all the abstractions which the users of his language might need. If a language is to be used at all, it is likely to be used to solve problems which its designer did not envision, and for which the abstractions embedded in the language are not sufficient. This paper presents an approach which allows the set of built-in abstractions to be augmented when the need for a new data abstraction is discovered. This approach to the handling of abstraction is an outgrowth of work on designing a language for structured programming. Relevant aspects of this language are described, and examples of the use and definitions of abstractions are given.

Sixty corporate websites selected from the Fortune Global 500 companies were examined in 2000 and again in 2001 to see if they provided support for automatic indexing. In particular, use of the robots.txt and Meta tags for "keywords" and "description" was examined. Slightly fewer than half of the sites provided one or both of these aids. Among sites providing indexing aids there was a clear under-representation of Asian sites. Nearly 80% of the sites used Java, suggesting a reasonable level of technical sophistication among website creators. About one-third of the sites used cookies, raising the possibility that repeat visitors might find the navigation of the site customized to their needs. Overall an increase in the use of indexing aids, especially Meta tags, represents one way in which web robots could index sites more quickly and thus improve overall index coverage of the web.

Most people do not use a formal geographical vocabulary, however they do use a wide variety of geographical terms on a daily basis. Identifiers such as 'Downtown' are components of a vernacular geography which is vastly more used than the coordinates and scientifically defined variables beloved of most professional analysts. Terms like these build into the jointly defined world-views within which we all act. Despite its importance for policymaking and quality of life, attention is rarely paid to this vernacular geography because it is hard to capture and use. This paper presents tools for capturing this geography, an example of the tools' use to define 'High Crime' areas, and an initial discussion of the issues surrounding vernacular data. While the problems involved in analysing such data are not to be underestimated, such a system aims to pull together professional and popular geographical understanding, to the advantage of both.

Well adapted to the loosely coupled nature of distributed interaction in large-scale applications, the publish/subscribe communication paradigm has recently received increasing attention. With systems based on the publish/subscribe interaction scheme, subscribers register their interest in an event, or a pattern of events, and are subsequently asynchronously notified of events generated by publishers. Many variants of the paradigm have recently been proposed, each variant being specifically adapted to some given application or network model. This paper factors out the common denominator underlying these variants: full decoupling of the communicating entities in time, space, and synchronization. We use these three decoupling dimensions to better identify commonalities and divergences with traditional interaction paradigms. The many variations on the theme of publish/subscribe are classified and synthesized. In particular, their respective benefits and shortcomings are discussed both in terms of interfaces and implementations.

Since the early 1960's, researchers have built a number of programming languages and environments with the intention of making programming accessible to a larger number of people. This article presents a taxonomy of languages and environments designed to make programming more accessible to novice programmers of all ages. The systems are organized by their primary goal, either to teach programming or to use programming to empower their users, and then, by each system's authors' approach, to making learning to program easier for novice programmers. The article explains all categories in the taxonomy, provides a brief description of the systems in each category, and suggests some avenues for future work in novice programming environments and languages.

Balancing the competing goals of collaboration and security is a difficult, multidimensional problem. Collaborative systems often focus on building useful connections among people, tools, and information while security seeks to ensure the availability, confidentiality, and integrity of these same elements. In this article, we focus on one important dimension of this problem — access control. The article examines existing access control models as applied to collaboration, highlighting not only the benefits, but also the weaknesses of these models.

Distributed data processing is becoming a reality. Businesses want to do it for many reasons, and they often must do it in order to stay competitive. While much of the infrastructure for distributed data processing is already there (e.g., modern network technology), a number of issues make distributed data processing still a complex undertaking: (1) distributed systems can become very large, involving thousands of heterogeneous sites including PCs and mainframe server machines; (2) the state of a distributed system changes rapidly because the load of sites varies over time and new sites are added to the system; (3) legacy systems need to be integrated — such legacy systems usually have not been designed for distributed data processing and now need to interact with other (modern) systems in a distributed environment. This paper presents the state of the art of query processing for distributed database and information systems. The paper presents the "textbook" architecture for distributed query processing and a series of techniques that are particularly useful for distributed database systems. These techniques include special join techniques, techniques to exploit intraquery parallelism, techniques to reduce communication costs, and techniques to exploit caching and replication of data. Furthermore, the paper discusses different kinds of distributed systems such as client-server, middleware (multitier), and heterogeneous database systems, and shows how query processing works in these systems.

Project Xanadu, the original hypertext project, is often misunderstood as an attempt to create the World Wide Web. It has always been much more ambitious, proposing an entire form of literature where links do not break as versions change; where documents may be closely compared side by side and closely annotated; where it is possible to see the origins of every quotation; and in which there is a valid copyright system — a literary, legal and business arrangement — for frictionless, non-negotiated quotation at any time and in any amount. The Web trivialized this original Xanadu model, vastly but incorrectly simplifying these problems to a world of fragile ever-breaking oneway links, with no recognition of change or copyright, and no support for multiple versions or principled re-use. Fonts and glitz, rather than content connective structure, prevail. Serious electronic literature (for scholarship, detailed controversy and detailed collaboration) must support bidirectional and profuse links, which cannot be embedded; and must offer facilities for easily tracking re-use on a principled basis among versions and quotations. Xanalogical literary structure is a unique symmetrical connective system for text (and other separable media elements), with two complementary forms of connection that achieve these functions — survivable deep linkage (content links) and recognizable, visible re-use (transclusion). Both of these are easily implemented by a document model using content lists which reference stabilized media. This system of literary structure offers uniquely integrated methods for version management, side-by-side comparison and visualizable re-use, which lead to a radically beneficial and principled copyright system (endorsed in principle by the ACM). Though dauntingly far from the standards which have presently caught on, this design is still valid and may yet find a place in the evolving Internet universe.

Hypertext links are connections between documents or parts of documents. Generally the ends of links are represented by some kind of a reference to a document or part of a document. When documents are moved or changed these references may cease to resolve to the correct places. This paper reflects on the causes of this problem and reviews techniques that may be used to maintain link integrity.

The aim of this review paper is to provide a "big picture snapshot" of the multiple facets of hypermedia linking. In providing this snapshot, the paper overviews key issues in both categorizing these facets and exploiting them to design effective implementations of links. The presentation is structured around the process of untying the perception of the link and its capabilities from the limitations of defining it in terms of the currently most pervasive implementation of the link, namely links in HTML. In the process, the paper draws on the work of Paul Thistlewaite on the linking issues for large volatile hyperbases.

Keeping multiple versions of the same electronic artifact is a necessity in many authoring fields, and a serious advantage in all of them. Hypermedia adds to that the issue of relationship management. This poses a few additional problems, especially conceptual ones, but it also provides a reliable and safe solution for the well-known problem of the referential integrity of links. The field of hypermedia has dealt with versioning issues for a long time, since Xanadu considered it a fundamental mechanism for its inner workings. Newer systems, and an important protocol for the WWW, WebDAV, constitute modern approaches to the problem.

The essential concepts of the relational data model are defined, and normalization, relational languages based on the model, as well as advantages and implementations of relational systems are discussed.

Clio is a system for managing and facilitating the complex tasks of heterogeneous data transformation and integration. In Clio, we have collected together a powerful set of data management techniques that have proven invaluable in tackling these difficult problems. In this paper, we present the underlying themes of our approach and present a brief case study.