AAC is one of two audio coding methods defined by the MPEG-2 standard. It is not backward compatible with MPEG-1 audio coding, which is why it is sometimes also referred to as the "non backward compatible" audio coding of MPEG-2. AAC provides more sophisticated audio coding than MPEG-2 BC audio coding (the other audio coding method of MPEG-2, better known as MP3), but it is not as widely spread.
Internet technical specifications often need to define a format syntax and are free to employ whatever notation their authors deem useful. Over the years, a modified version of BNF, called ABNF, has been popular among many Internet specifications. It balances compactness and simplicity with reasonable representational power.
An ACE a string of characters resulting from a particular algorithm for transforming multilingual character information into an ASCII-based alphanumeric form acceptable by the existing DNS. This means that an ACE encoded string must conform to the LDH restrictions for strings.
ActiveX is the name Microsoft has given to a set of object-oriented concepts, technologies, and tools. It is important to notice that ActiveX is not a specific technology, but a brand name, what it's applied to can vary over time. However, the main technology is COM. Used in a network with a directory and additional support, COM becomes the DCOM. The main object that is created when writing a program to run in the ActiveX environment is a component, a self-sufficient program that can be run anywhere in the ActiveX network. This component is known as an "ActiveX control". An ActiveX control is roughly equivalent to a applet. One important difference is that an ActiveX control must be compiled for a specific platform, while an applet is platform-independent.
AES is the replacement of DES, because recent research and attacks have shown that DES is not as safe as necessary for some applications. AES has been chosen from a number of canidates based on criteria such as efficiency, robustness, and cryptographical safety.
AIFF is a proprietary Audio Format developed by Apple. The format can store monaural or multichannel sampled sounds in a range of sample rates and sample resolutions. Although originally AIFF did not support compressed audio data, a new version of the format called AIFF-C has been defined which allows compression.
AIFF-C is an extended version of Apple's AIFF Audio Format. It incorporates compression features, which have not been included in the original AIFF Audio Format.
ANSI, founded in 1918, does not itself develop American National Standards; rather it facilitates development by establishing consensus among qualified groups. The Institute ensures that its guiding principles (consensus, due process, and openness) are followed by the more than 175 distinct entities currently accredited. ANSI promotes the use of US standards internationally, advocates US policy and technical positions in international and regional standards organizations, and encourages the adoption of international standards as national standards where these meet the needs of the user community.
The Apache Software Foundation is a collaborative software development effort aimed at creating a robust, commercial-grade, feature-full, and freely-available source code implementation of an HTTP Server. The project is jointly managed by a group of volunteers located around the world, using the Internet and the WWW to communicate, plan, and develop the Server and its related documentation. In addition, hundreds of users have contributed ideas, code, and documentation to the project. In addition to the well-known and established Apache HTTP Server, the Cocoon project aims at developing a next-generation HTTP Server integrating XML technologies.
An API is an Interface which is used for accessing an application or a service from a program. An API makes it possible to use programs from within programs, therefore it is the foundation for modular systems with clearly defined Interfaces between separate components. In a way, an API can be regarded as the local equivalent of a Protocol, because it is used for the same purposes and defines the same things (the possible interactions between components, and the data that is exchanged while interacting). However, traditionally APIs are used for Interfaces on one computer, while Protocols are used for distributed scenarios.
An applet is a special type of Java program that can be included in an HTML page, much as an image can be included. When using a Java-compatible Browser to view a page that contains an applet, the applet's code is transferred to and executed by the Browser. Since an applet is platform-independent, the same applet can be executed on all types of platforms, as long as they support Java.
The ARPANET is the precursor to the Internet. It was established through an ARPA-funded research program in 1968 and provided the foundation of the Internet by providing the Protocols as well as the infrastructure. The original ARPANET grew into the Internet.
ASCII specifies the coding of space and a set of 94 characters (letters, digits and punctuation or mathematical symbols) suitable for the interchange of english language documents. ASCII forms the basis for most computer code sets and is the american national version of ISO 646.
Microsoft's ASF is an extensible file format designed to store synchronized multimedia data. It supports data delivery over a wide variety of networks and protocols while still proving suitable for local playback. The explicit goal of ASF is to provide a basis for industry-wide multimedia interoperability. Each ASF file is composed of one or more media streams. The file header specifies the properties of the entire file, along with stream-specific properties. Multimedia data, stored after the file header, references a particular media stream number to indicate its type and purpose. The delivery and presentation of all media stream data is synchronized to a common time-line. ASF's functionality is similar to the one provided by Apple's QuickTime.
ASN.1 defines a method for the specification and encoding of arbitrary data structures. ASN.1 is part of the OSI model of protocol layers, it is located within the "presentation layer" (layer 6). The approach of ASN.1 is to define an abstract syntax for the specification of structured data, and encoding rules for transforming structured data into a binary representation (which can then be exchanged). BER is the oldest encoding for ASN.1, and a subset of it (known as DER) is used for X.509 Certificates.
An ASP is providing an application to be used by ASP customers. In contrast to traditional software distribution, the software that provides the service is run by the ASP, and it is accessed remotely (and thus never downloaded or installed) by the customers. A common way for providing such services is over the WWW, where the application is accessed via various HTML pages which in their entirety make up the GUI. One of the best known ASPs is HotMail, which makes an Email application available over the WWW.
Microsoft's AVI file format is used for storing audio and/or video information. It is a common format for audio and video files within PC environments. Being a proprietary technology, AVI can be functionally compared to Apple's QuickTime.
B2B is the use of computer applications communicating over networks to allow businesses to complete a transaction or part of a transaction. In contrast to B2C, B2B describes the interaction of businesses. While the amount of B2C transactions using WWW-based technologies (often called online shopping) exceeds the amount B2B transactions, the total value of the B2B transactions is much larger than that of the B2C transactions, because typically B2B transactions are of much greater value than B2C transactions.
Base64 encoding is designed to represent arbitrary sequences of octets in a form that need not be humanly readable. The encoding and decoding algorithms are simple, but the encoded data are consistently only about 33 percent larger than the unencoded data. In Base64, a 65-character subset of ASCII is used, enabling 6 bits to be represented per printable character. Base64 is virtually identical to the encoding used in PEM applications.
BC audio coding is one of two audio coding methods defined by the MPEG-2 standard. It is backward compatible with MPEG-1 audio coding. BC is comprised of three different and increasingly complex layers, and if all three layers are used, it is the audio coding most commonly referred to as MP3. MPEG-2 also defines a non backward compatible audio coding, which is known as AAC.
BibTeX is a simple but popular Format and program for storing and processing bibliographic references. In almost all cases it is used together with LaTeX, but it can also be used to create other kinds of output.
BibTeXML is an XML representation for BibTeX data. The advantage of BibTeXML over the standard BibTeX format is the availability of tools for processing XML data in general, and the ease of integration of BibTeXML into an XML-based environment.
BIND implements an Internet name server. It consists of a server and a resolver library. BIND is an implementation of DNS, both Server and Client. Development of BIND is funded by the ISC. BIND has been ported to Windows and VMS, but is most often found on Unix. BIND source code is freely available and very complex; most of the development on the DNS Protocols is based on this code; and most Unix vendors ship BIND-derived DNS implementations. As a result, the BIND name server is the most widely used name server on the Internet.
BNF is a formal meta-syntax used to express con text-free grammars. BNF is one of the most commonly used meta-syntactic notation s for specifying the syntax of programming languages, command sets, PDUs, and similar things. However, pure BNF is rather limited, so the two variations EBNF and ABNF have become more popular.
A Bridge is a device that connects networks segments on the data link layer of the network. Related to Bridges are Repeaters, Routers, and Gateways, which also connect network segments, but on different layers of the networking architecture.
A CA is an authority trusted by one or more users to create and assign Certificates. Optionally the CA may create the user's keys. It is important to note that the CA is responsible for the Certificates during their whole lifetime, not just for issuing them.
Canonical XML refers to XML that is in canonical form. XML canonicalization is a process that generates the Canonical XML of a given XML document. XML specifies the syntax of XML documents. XML Namespaces specifies additional syntax and semantics for XML documents. Because of the syntax of XML, it is possible for XML documents which are equivalent for the purposes of many applications to differ in physical representation. For example, they may differ in whitespace occurrences, their entity structure, attribute ordering, and character encoding. Canonical XML establishes a method for determining whether two documents are identical, or whether an application has not changed a document, except for transformations permitted by XML and XML Namespaces.
Former name of the ITU before it was renamed in 1993.
A ccTLD is a DNS TLD identifying domain names for a given country. The country-codes being used are the two letter codes defined by ISO 3166. The IANA is not in the business of deciding what is and what is not a country. The selection of the ISO 3166 list as a basis for ccTLDs was made with the knowledge that ISO has a procedure for determining which entities should be and should not be on that list.
Certificates are digital documents attesting to the binding of a public key to an individual or other entity. They allow verification of the claim that a given public key does in fact belong to a given individual. Certificates help prevent someone from using a phony key to impersonate someone else. In their simplest form, Certificates contain a public key and a name. As commonly used, a Certificate also contains an expiration date, the name of the CA that issued the Certificate, a serial number, and perhaps other information. Most importantly, it contains the digital signature of the certificate issuer. The most widely accepted format for certificates is X.509, thus, Certificates can be read or written by any application complying with X.509.
A Display Standard referring to a video adapter capable of a resolution of up to 320 by 200 pixels.
CGI is an API for interfacing external applications with information Servers, such as an HTTP Server. CGI can be used with any Programming Language. A plain HTML document that the HTTP Server retrieves upon a request is static, which means it exists in a constant state, for example as a text file that does not change. A CGI program, on the other hand, is executed in real-time, so that it can generate dynamic information.
CGM is a machine and Operating System independent interchange format that provides elements to represent geometric graphics (eg, polygons or circles) and raster graphics (eg, pixel arrays). It consists of a functional specification and multiple encodings for different purposes. There are three standardized encodings for CGM, clear-text, character and binary. Clear-text is human-readable. Character encoding is more compact, but still uses ASCII characters, so that it can be interchanged without Protocol problems. The binary encoding is more compact still, and quick to encode and decode, but completely unreadable.
With the introduction of persistent connections in HTTP/1.1, the length of a resource which is sent in a response can no longer be implicitly signaled by closing the connection. However, for the majority of resources, the length is known in advance and can be given in the HTTP's Content-Length header field. For all other resources (such as dynamically created content), Chunked Encoding can be used. Chunked Encoding transfers the message body as a sequence of chunks of known length.
CLF is a log file Format for HTTP Servers, containing information about the host, identification of the user (if available), authorized user-name (if available), date, the request line itself, and the returned status and number of bytes. Although most HTTP Servers can be configured to produce other Formats of log files, many tools exist to analyze CLF files, so custom log file Formats should only be used if absolutely necessary.
CMS is used to digitally sign or encrypt arbitrary messages. CMS describes an encapsulation syntax for data protection. It supports digital signatures and encryption. The syntax allows multiple encapsulation, so one encapsulation envelope can be nested inside another. Likewise, one party can digitally sign some previously encapsulated data. It also allows arbitrary attributes, such as signing time, to be authenticated along with the message content, and provides for other attributes such as counter-signatures to be associated with a signature.
Cocoon is an XML publishing framework based on XSLT. Designed for performance and scalability around pipelined SAX processing, Cocoon offers a flexible environment based on the separation of content, logic, and style. Cocoon's centralized configuration system and caching are designed to create, deploy, and maintain scalable XML applications. Cocoon interacts with most data sources, including File Systems, RDBMSs, LDAP, XML Database Management Systems , and network-based data sources. It adapts content delivery to the capabilities of different output formats such as HTML, WML, PDF, SVG, RTF, and others. Cocoon can be executed as a servlet as well as through a command line interface.
A Codec is an entity that is responsible for encoding and decoding some Format. Codecs can be implemented in hardware or software. A typical example is an MP3 Codec, which is responsible for decoding an MP3 audio stream for playback, or encoding it for transmission or storage using the compact MP3 Audio Compression.
Microsoft's COM is a software architecture that allows applications to be built from binary software components. COM is the underlying architecture that forms the foundation for higher-level software services, like those provided by OLE. COM defines a binary standard for function calling between components, a way for components to dynamically discover the interfaces implemented by other components, and a mechanism to identify components and their interfaces uniquely.
Content Negotiation is an HTTP mechanism which is used to make a selection between different representations for a resource. Different representations can be characterized by language, quality, encoding, or other parameters which do not affect the content of a resource. HTTP defines two types of Content Negotiation, Server-driven and agent-driven. In Server-driven Content Negotiation, the HTTP Server makes the selection and sends a response with the representation of a requested resource which it thinks matches the user's needs, based on the request, available representations, and other information. In agent-driven Content Negotiation, the HTTP Server responds with a list of all representations and the HTTP Client (or the user) makes the selection and requests the selected representation.
Originally introduced by Netscape Communications, Cookies are a general mechanism which HTTP Server side applications, such as CGI scripts, can use to both store and retrieve information on the HTTP Client side of the connection. Basically, Cookies can be used to compensate for the stateless nature of HTTP. The addition of a simple, persistent, client-side state significantly extends the capabilities of WWW-based applications.
CORBA describes the architecture of a middleware platform that supports the implementation of applications in distributed and heterogeneous environments. The CORBA standard is issued by OMG. In contrast to other middleware platforms such as Microsoft's DCOM, CORBA is a specification that does not prescribe any specific technology.
XML Schema Languages cover different areas of XML schema aspects, such as grammar-based schemas (e.g., DTD and XML Schema and rule-based schemas (e.g., Schematron). CRVX is a specialized and simple schema language for specifying character repertoire constraints for XML documents. It is meant as a complement for other schema languages which are often geared towards structural contraints for XML documents. CRVX is based on the Unicode character set which is the foundation of XML.
CSS is a Style Sheet Language which has been primarily designed for HTML, even though it can also be used for XML documents. While HTML should be used to define the contents of a WWW page, CSS is the language for specifying the presentation aspects of it. The two main advantages of HTML with CSS over HTML without CSS are the clear separation of content and presentation (which makes the automated processing of WWW pages much easier and also enables users to apply their own style sheets instead of the defaults provided by their Browser or a WWW page's designer), and the greatly enhanced formatting capabilities with CSS.
CSS-OM is a model of how CSS style sheets can be accessed and manipulated through a DOM interface. CSS-OM thus is relevant for both CSS and DOM, and is important if CSS should be accessed and manipulated from within an application.
In the first implementation of CSS in Netscape Communications's Navigator, additional functionality was included which added absolute positioning and layering to the initial CSS1 specification. Netscape Communications submitted a working draft as a proposal for these positioning features to W3C.
DAP is the original protocol for accessing X.500. Since DAP is based on OSI and rather complex, a simplified variant of DAP based on the TCP has been designed, which is called LDAP. Today this simpler variant is more popular than DAP itself.
DARPA, until 1973 known as ARPA, is the main source for research funds in the United States. In particular, the Internet (its first infrastructure as well as the protocol suite) originated from the ARPANET, a network which was first designed for US military purposes with the primary design goal to be robust.
DCE is an industry-standard, vendor-neutral set of distributed computing technologies. It provides security services to protect and control access to data, name services that make it easy to find distributed resources, and a highly scalable model for organizing widely scattered users, services, and data. DCE runs on all major computing platforms and is designed to support distributed applications in heterogeneous hardware and software environments.
DCOM is a Protocol that enables software components to communicate directly over a network in a reliable, secure, and efficient manner. Previously called OLE, DCOM is designed for use across multiple network transports, including Internet Protocols such as HTTP. DCOM is based on DCE RPC and COM.
DES was originally developed at IBM. DES has been extensively studied since its publication and is the most well-known and widely used cryptosystem in the world. DES is an algorithm implementing Secret-Key Cryptography, when used for communications, both sender and receiver must know the same secret key, which is used both to encrypt and decrypt the message. DES can also be used for single-user encryption, such as to store files on a hard disk in encrypted form. In a multi-user environment, secure key distribution may be difficult. Public-Key Cryptography provides an ideal solution to this problem. Even though DES has been cryptographically enhanced by using three encryption rounds, yielding 3DES, the general consensus is that DES encryption is too weak for some scenarios, and the stronger AES will eventually replace DES.
DHTML does not refer to a specific version or a specific feature of HTML. It is an expression which is commonly used to refer to all features of HTML which go beyond the presentation of static documents. The most popular mechanisms which are encompassed by the term DHTML are CSS, scripts (in most cases ECMAScript-based languages, embedded with the <SCRIPT> element), and objects (embedded with the <OBJECT> element). DHTML also often refers to Browser-specific extensions of particular mechanisms, such as extensions to the basic scripting methods, or the ability to dynamically download fonts. The "glue" between the different components which make up DHTML (mainly HTML, CSS, and a scripting language) is provided by DOM.
Diffie-Hellman key agreement describes a method whereby two parties, without any prior arrangements, can agree upon a secret key that is known only to them (and, in particular, is not known to an eavesdropper listening to the dialogue by which the parties agree on the key). This secret key can be used, for example, to encrypt further communications between the parties using Secret-Key Cryptography. The intended application of this standard is in Protocols for establishing secure connections. Details on the interpretation of the agreed-upon secret key are outside the scope of Diffie-Hellman key agreement, as are details on sources of the pseudo-random bits required by this method. The Diffie-Hellman key exchange is vulnerable to a middleperson attack. This vulnerability is due to the fact that Diffie-Hellman key exchange does not authenticate the participants.
DNS is a distributed, replicated, data query service mainly used on the Internet for translating host names to IP addresses. The three main components of DNS are: the domain name space and resource records, which are specifications for a tree structured name space and data associated with the names; name servers, which are server programs which hold information about the domain tree's structure and set information; and resolvers, being programs that extract information from name servers in response to client requests.
The DOI system is a mechanism for marking digital objects in order to facilitate E-Commerce and enable copyright management in a digital environment. DOI not only provides a unique identification for digital content, but also a way to link users of the materials to the rights holders themselves to facilitate automated digital commerce. The underlying technology of DOI is the Handle System, which associates each DOI name with one or more locations where the object may be found.
DOM is a platform- and language-neutral API that allows programs and scripts to dynamically access and update the content, structure and style of WWW documents (currently, definitions for HTML and XML documents are part of the specification). The document can be further processed and the results of that processing can be incorporated back into the presented page. DOM is a tree-based API to documents, which requires the whole document to be represented in memory while processing it. A simpler alternative to DOM is the event-based SAX, which can be used to process very large XML documents that do not fit into the memory available for processing.
DSL is a technology for bringing high-bandwidth information to homes and small businesses over ordinary copper PSTN lines. The widely used term xDSL refers to different variations of DSL, such as ADSL, HDSL, VDSL and SDSL. Most DSL technologies require that a signal splitter be installed at a home or business, requiring the expense of a phone company visit and installation. However, it is possible to manage the splitting remotely, this has been standardized as G.Lite.
DSA was published by NIST in the DSS standard. DSA is for authentication only. In DSA, signature generation is faster than signature verification, whereas in RSA, signature verification is faster than signature generation (if the public and private exponents, respectively, are chosen for this property, which is the usual case). NIST claims that it is an advantage of DSA that signing is faster, but many people in cryptography think that it is better for verification to be the faster operation.
DSSSL is an international standard for specifying document transformation and formatting in a platform- and vendor-neutral manner. DSSSL can be used with any document format for which a property set can be defined according to the HyTime standard. In particular, DSSSL can be used to specify the presentation of documents marked up according to SGML. DSSSL consists of two main components, a transformation language and a style language. The transformation language is used to specify structural transformations on SGML source files. The transformation language can also be used to specify the merging of two or more documents, the generation of indexes and tables of contents, and other operations.
DSSSL-Lite was an early approach to define a profile (ie, a functional subset) of DSSSL in an attempt to create a version of DSSSL which is less complex and still powerful enough to be sufficient for a large number of applications. DSSSL-Lite never became an actual standard, but the work on it was used as input for the DSSSL-O activity.
Based on results from the DSSSL-Lite activity, DSSSL-O was an attempt to define a profile (ie, a functional subset) of DSSSL. This profile should be less complex than full DSSSL and particularly suited to the needs of online publishing. DSSSL-O never became an actual standard, but it was used as the base for XSL, which is used as the style sheet language for XML documents.
A DTD is one component inside an SGML or XML environment. It defines the syntactic rules according to which a document can be composed. There are no semantics associated with the elements and attributes defined in a DTD, although normally the names chosen for elements and attributes will have some meaning to them. Using a DTD and an XML Processor, a document can be validated against the DTD, which means it can be tested whether it conforms to a given DTD. HTML is one example of an SGML DTD (which has been reformulated as an XML DTD in XHTML).
The Dublin Core is a Meta Data element set intended to facilitate discovery of electronic resources. Originally conceived for author-generated description of WWW resources, it has attracted the attention of formal resource description communities such as museums, libraries, government agencies, and commercial organizations. One example application of the Dublin Core elements is OEB.
An EBNF is any variation on the basic BNF meta-syntax notation with (some of) the following additional constructs: square brackets surrounding optional items, asterisk suffix for a sequence of zero or more of an item, plus-sign suffix for one or more of an item, curly brackets enclosing a list of alternatives, and super- and subscripts indicating the number of possible occurrences. All these constructs can be expressed in plain BNF using extra productions and have been added for readability and succinctness.
ECMA is an international, europe-based industry association founded in 1961 and dedicated to the standardization of information and communication systems. Many ECMA standards have been accepted as a base for international and european standards. To ensure close cooperation ECMA has established formal liaisons with all european and international standardization bodies. ECMA standards are developed by highly qualified experts from information technology and telecommunication industry with the commitment to provide in a consensus mode technical solutions ready for implementation in product development and conformance testing.
ECML provides a set of simple guidelines for WWW merchants that will enable electronic wallets from multiple vendors to fill in their HTML Forms. ECML defines a number of simple field types for B2C scenarios, which should be used by HTML Forms for naming fields. Using these standardized fields, mechanisms on the Browser side (such as electronic wallets) can automatically identify and fill out forms for the user, making transactions for the user more easy.
EDI is the computer-to-computer exchange of business data in standard formats. In EDI, information is organized according to a specified format set by both parties, allowing an automated computer transaction that requires no human intervention or rekeying on either end. The information contained in an EDI transaction set is, for the most part, the same as on a conventionally printed document. EDI standards in the US are set and published by the ASC X12 committee of ANSI. International EDI standards are known as EDIFACT standards.
A Display Standard referring to a video adapter capable of a resolution of up to 640 by 350 pixels.
ESMTP describes a framework for extensions of SMTP. SMTP still provides the basic mechanism for exchanging Email messages, but it has become apparent that it lacks some important functionality. Instead of defining a revised but static new version of SMTP, ESMTP defines a mechanism how extensions can be integrated into the basic Protocol, and how these extensions can be used in an interoperable way.
Many digital cameras store images using EXIF compressed files. EXIF compressed files use JPEG for Image Compression. This means the image data can be read by any application supporting JPEG. In addition, EXIF stores Meta Data within application segments at the beginning of the file, and uses sRGB as the default color space. It is recommended that EXIF image files should be named and arranged in directories according to the DCF specification.
FAQs are collections of questions and answers that frequently occur for a specific subject. FAQ have a long tradition in Usenet News newsgroups, where they are periodically posted for bringing new subscribers up-to-date.
FastCGI is an extension of the CGI which eliminates its drawbacks and provides high performance, while remaining highly compatible with existing CGI applications. FastCGI is conceptually very similar to CGI, with two major differences. As the first difference, FastCGI processes are persistent, after finishing a request, they wait for a new request instead of exiting. The second difference is that, instead of using Operating System environment variables and pipes, the FastCGI protocol multiplexes the environment information, standard input, output and error over a single full-duplex connection. This allows FastCGI programs to run on remote machines, using TCP connections between the HTTP Server and the FastCGI application.
A Firewall is a special kind of Gateway that is used to block certain types of network traffic (typically, network traffic that is potentially dangerous). Most Firewalls work as packet filters, comparing the passing packets to a set of filter rules. Typically, the comparison performed by the packet filter involves the source address, the source Port, the destination address, and the destination Port. Filtering on source and destination addresses grants control over who may communicate with the internal network. All traffic from undesirable networks can be screened out. Ports, on the other hand, are used to distinguish network services. By filtering out a Port, it is possible to deny the outside world access to a service offered on the internal network.
A FQDN is a domain name that includes all higher level domains relevant to the entity named.
A FQHN is either the FQDN of a host (ie, a completely specified domain name ending in a TLD), or the numeric IP address of a host.
FTP is a Protocolfor file transfer between hosts on the Internet. The primary function of FTP is to transfer files efficiently and reliably among hosts and to allow the convenient use of remote file storage capabilities. The objectives of FTP are to promote sharing of files (computer programs and/or data), to encourage indirect or implicit (via programs) use of remote computers, to shield users from variations in file storage systems among hosts, and to transfer data reliably and efficiently. FTP, though usable directly by a user at a terminal, is designed mainly for use by programs.
A Gateway is a device that connects networks segments on any layer higher than the network layer of the network (typically on the application layer). Related to Gateways are Repeaters, Bridges, and Routers, which also connect network segments, but on different layers of the networking architecture.
GIF is a data stream-oriented Image Format used to define the transmission protocol of LZW-encoded bitmap data. GIF images may be up to eight bits (256 colors) in depth and are always compressed. Despite the fact that GIF supports only 8-bits worth of colors, and the multimedia extensions introduced in the GIF89a release have not been widely utilized, GIF still remains a popular choice for storing lower resolution image data. Any software created or modified after 1994 that supports the capability of reading and/or writing GIF files must obtain a patent license agreement from Unisys Corporation. For publishing on the WWW, JPEG is a good companion format for photo-realistic images, while PNG has been designed to replace GIF in the long run.
GIOP is the abstract Protocol which is used for communications between CORBA ORBs. It specifies the transfer syntax and a standard set of message formats for ORB interoperation over any connection-oriented transport Protocol. GIOP is designed to be simple and easy to implement, while still allowing for reasonable scalability and performance.
The Gopher Protocol is designed primarily to act as a distributed document delivery system. While documents (and services) reside on many Servers, Gopher Client software presents users with a hierarchy of items and directories much like a file system. In fact, the Gopher Interface is designed to resemble a file system since a file system is a good model for locating documents and services. The user sees what amounts to one big networked information system containing primarily document items, directory items, and search items (the latter allowing searches for documents across subsets of the information base). Since the WWW allows greater flexibility in the structure and presentation of distributed information, the usage of gopher services and the number of gopher servers is getting smaller.
GPRS represents the first implementation of packet switching within The GSM, which is essentially a circuit-switched technology. Using GPRS will enable users to send and receive data at speeds up to 115kbit/s. GPRS is very efficient in its use of scarce spectrum resources and enables GPRS operators to introduce a wide range of value added services. GPRS is ideal for bursty data applications such as Email or Internet access, and can also enable "virtual permanent connections" to data sources, allowing information to arrive rather than being sought. This cannot be achieved using standard circuit-switched networks.
GSM is a digital cellular communications system. It was developed in order to create a common european mobile telephone standard but it has been rapidly accepted worldwide. GSM was designed to be compatible with ISDN services. The disadvantage of this design is the focus on circuit-switched technologies, which currently makes GSM less than ideally suited for mobile data access. However, with the introduction of GPRS in newer versions of the GSM standard, GSM becomes capable of handling packet-switched traffic.
A gTLD is a DNS TLD which is not specific to a country. Each of the gTLDs was created for a general category of organizations. Generally, under the gTLDs the structure is very flat. That is, many organizations are registered directly under the gTLD, and any further structure is up to the individual organizations.
A GUI is the usual way to access a computer. The most common GUIs are the Windows GUI, and the MacOS GUI. GUIs usually employ a number of predefined design elements (such as pull-down menus and buttons) which are used to implement specific functions. The most common Browsers (Navigator and IE) also implement GUIs, in this case for accessing the WWW. Examples for non-GUI Browsers are text-based browsers such as Lynx, or entirely non-visual browsers (for example using speech synthesis techniques).
The Handle System is a comprehensive system for assigning, managing, and resolving persistent Identifiers, known as "handles", for digital objects and other resources on the Internet. Handles can be used as URNs. The Handle System includes an open set of Protocols, a name space, and an implementation of the Protocols. The Protocols enable a distributed computer system to store handles of digital resources and resolve those handles into the information necessary to locate and access the resources. This associated information can be changed as needed to reflect the current state of the identified resource without changing the handle, thus allowing the name of the item to persist over changes of location and other state information. Combined with a centrally administered naming authority registration service, the Handle System provides a general purpose, distributed global naming service for the reliable management of information on networks over long periods of time.
The High Sierra format is a logical format for CD-ROM media. It was used mainly between 1986 and 1988, after 1988 it was replaced by the ISO 9660 standard for the logical format on CD-ROM media (High Sierra and ISO 9660 are identical in content, but the exact format is different).
HTML is a simple markup language used to create hypertext documents that are platform independent. HTML documents are SGML documents with generic semantics that are appropriate for representing information from a wide range of domains. For example, HTML markup can represent Usenet News, Email, documentation, menus of options, database query results, simple structured documents with in-lined images, and hypertext views of existing bodies of information.
HTTP is the protocol used for information exchange on the WWW. HTTP defines how messages are formatted and transmitted, and what actions a HTTP Server and an HTTP Client (which in most cases is a Browser) should take in response to various messages. HTTP uses a reliable, connection-oriented transport service such as the TCP. HTTP is a stateless Protocol, where each request is interpreted independently, without any knowledge of the requests that came before it.
HTTP is being used for an increasing number of applications involving distributed authoring, collaboration, printing, and various RPC-like Protocols. The HTTP Extension Framework is an extension mechanism for HTTP designed to address the tension between private agreement and public specification, and to accommodate extension of HTTP Clients and HTTP Servers by software components.
In the context of the WWW, an HTTP Proxy is an intermediary program which acts as both an HTTP Server and an HTTP Client, receiving a request from a Client (in most cases a Browser) and then acting as an HTTP Client and making requests on behalf of other HTTP Clients. However, requests to an HTTP Proxy can also be serviced internally, for example if the HTTP Proxy uses its Cache instead of sending a request to the origin HTTP Server. In order to use an HTTP Proxy, the HTTP Client's request has to be explicitly addressed to the HTTP Proxy, which then sends a request to the origin HTTP Server. An HTTP Proxy may also perform a protocol conversion, for example a Browser may send an HTTP request to the HTTP Proxy referencing an FTP resource, and the HTTP Proxy then acts as FTP Client to retrieve the resource from the FTP Server using FTP, and eventually the resource is sent back from the HTTP Proxy to the Browser using HTTP.
HTTPS is a secure way of using HTTP. HTTP provides almost no security features, it contains only basic authentication mechanisms, and no support for privacy. HTTPS solves this problem by replacing HTTP's transport layer, the insecure TCP, with SSL, a secure transport layer. In the near future, SSL will probably be replaced by the more general TLS protocol, but it is very unlikely that the already established name of HTTPS will be changed to reflect this change.
I18N is the process of designing an application so that it can be adapted to various languages and regions without engineering changes. The abbreviation is based on the fact that the rather lengthy word 'internationalization' starts with an 'i' followed by 18 characters followed by an 'n'. An internationalized system has the following characteristics: after L10N, the same executable can run worldwide; textual elements, such as status messages and the GUI component labels, are not hardcoded in the program (instead they are stored outside the source code and retrieved dynamically); support for new languages does not require recompilation; culturally-dependent data, such as dates and currencies, appear in formats that conform to the end user's region and language; L10N can be done quickly.
The IAB is the technical body that oversees the development of the Internet Protocol suite. It has two task forces, the IETF and the IRTF.
ICMP is at the same Protocol layer as IP, its purpose is to transmit information needed to control IP traffic. It is used mainly to provide information about routes to destination addresses. ICMP redirect messages inform hosts about more accurate routes to other systems, whereas ICMP unreachable messages indicate problems with a route. Additionally, ICMP can cause TCP connections to terminate gracefully if the route becomes unavailable. The ping command is a commonly-used ICMP-based service.
IDEA is a symmetric block cipher. The speed of IDEA in software is similar to that of DES. One of the principles during the design of IDEA was to facilitate analysis of its strength against differential cryptanalysis. IDEA is considered to be immune from differential cryptanalysis. In addition, no linear cryptanalytic attacks on IDEA have been reported and there is no known algebraic weakness in IDEA.
IETF is a large open international community of network designers, operators, vendors, and researchers concerned with the evolution of the Internet architecture and the smooth operation of the Internet. It is open to any interested individual. The actual technical work of the IETF is done in its working groups, which are organized by topic into several areas (eg, routing, transport, security, etc.).
IIOP is the most commonly used Protocol for communications in CORBA. IIOP is a Protocol for the Client/Server-Model between two CORBA implementations. In a similar way to HTTP, which uses URIs to locate Servers and in requests from Clients to Servers, CORBA uses an IOR for identifying remote objects. IORs can be used to invoke operations on remote CORBA systems, using IIOP for communications.
IMAP is a Email Protocol allowing a Client to access and manipulate Email messages on a Server. It permits manipulation of remote message folders (mailboxes) in a way that is functionally equivalent to local mailboxes. IMAP includes operations for creating, deleting, and renaming mailboxes; checking for new messages; permanently removing messages; searching; and selective fetching of message attributes, texts, and portions thereof. It does not specify a means of posting mail; this function is handled by a mail transfer protocol such as SMTP. IMAP is newer and more powerful than POP, which is used for the same application area.
The Internet is the entirety of all computers which are interconnected (using various physical Networking techniques) and employ the Internet Protocol suite on top of their networking systems.
An IOR is a data structure that stores information needed to locate and communicate with a CORBA object over one or more Protocols. For example, an IOR containing IIOP information stores IP address and TCP Port number information.
IP is specifically limited in scope to provide the functions necessary to deliver a package of bits (an Internet datagram) from a source to a destination over an interconnected system of networks. There are no mechanisms to augment end-to-end data reliability, flow control, sequencing, or other services commonly found in host-to-host Protocols. In most cases, TCP is used on top of IP.
Although IP is the most visible Protocol of the Internet, there are many other Protocols which are also part of the Internet architecture and which also have to be changed when making the transition from IPv4 to IPv6. In the context of IPv6, there are also a number of protocols which are new to the Internet architecture. The common practice is to use the term IPng to refer to all protocols which have to be changed or added when switching to IPv6.
IPR are temporary grants of monopoly intended to give economic incentives for innovative activity. IPR exist in the form of patents, copyrights, and trademarks.
IPv6 is a new version of IP which is designed to be an evolutionary step from IPv4 (commonly referred to simply as IP). It can be installed as a normal software upgrade in Internet devices and is interoperable with the current IPv4. Its deployment strategy was designed to not have any "flag" days. IPv6 is designed to run well on high performance networks (eg, ATM) and at the same time is still efficient for low bandwidth networks (eg, Wireless Interfaces). In addition, it provides a platform for new Internet functionality (such as resource reservation capabilities) that will be required in the near future.
An IRI is a generalized form of URI that may contain non-ASCII characters.
The IRTF is composed of a number of focused, long-term and small research groups. These groups work on topics related to Internet Protocols, applications, architecture and technology. The IRTF focuses on longer term research issues related to the Internet, while the parallel organization, the IETF, focuses on the shorter term issues of engineering and standards making.
The ISBN is a nine- or ten-digit number which identifies a specific book title and is recognized worldwide. Publishers assign ISBNs to books to simplify and expedite their ordering and purchase. An ISBN number can often be found on the back of the title page of a book or at the bottom of the back cover, though many older books do not have ISBNs. Sometimes more than one book has the same ISBN, as is frequently the case with books in a series. Book records for books in a series may also contain an ISSN for the series. Separate ISBNs are usually assigned for each format of a book (such as hard-cover or paperback). Newer books frequently also have an EAN-encoded version of the ISBN on their cover.
The ISO 9660 format is a logical format for CD-ROM media. It was standardized in 1988 and replaced the High Sierra standard for the logical format on CD-ROM media (ISO 9660 and High Sierra are identical in content, but the exact format is different).
The ISSN is an internationally accepted code which identifies serial publications. It is an eight-digit number consisting of seven digits plus a check digit which enables a computer to recognize when the number is incorrectly cited. The check digit may be an "X", otherwise the ISSN is fully numeric. An ISSN may be used as control numbers for serial titles in automated systems, for example for identifying titles, ordering, checking in, and claiming by libraries and subscription agents. It may be used to ensure more accurate serials citation by scholars, researchers, abstractors and librarians and is particularly helpful when distinguishing between serials with identical titles. An increasingly important use of the ISSN is as a component in EAN barcodes for magazines.
ITU is an International Organization, within which the public and private sectors cooperate for the development of telecommunications. ITU adopts international regulations and treaties governing all terrestrial and space uses of the frequency spectrum as well as the use of the geostationary-satellite orbit, within which countries adopt their national legislation. It also develops standards to facilitate the interconnection of telecommunication systems on a worldwide scale regardless of the type of technology used.
JAR is a platform-independent Format that aggregates many files into one. Multiple Java applets and their requisite components (class files, images, and sounds) can be bundled in a JAR file and subsequently downloaded to a Browser in a single HTTP transaction, improving the download speed. The JAR format also supports compression, which reduces the file size, further improving the download time . In addition, the applet author can digitally sign individual entries in a JAR file to authenticate their origin.
Java is a general-purpose object-oriented Programming Language. Java is interesting in the context of the WWW because it is compiled into Java "bytecode", which is executed on a JVM. This design makes Java programs platform-independent, and Java applets, a special form of Java programs, can be integrated into WWW documents. Most Browsers today contain a JVM and a run-time environment for applets.
JAXP is an API for XML parsing and processing. It is an abstraction layer (ie, an API for other APIs) which can be used to access XML-specific functionality from within Java programs. JAXP supports parsing XML documents using the DOM or SAX APIs, and processing XML documents with XSLT using the TrAX API.
JBIG is the name of the committee that designed the Image Compression algorithm that is also called JBIG.
JBIG is an Image Compression standard that is mainly intended as an improvement of ITU's G3 Fax and G4 Fax recommendations for facsimile transmission. Apart from coding bilevel (ie, black and white) images, JBIG can also be used for coding grayscale and color images with limited numbers of bits per pixel. It uses a lossless compression algorithm which typically reduces the size of the uncompressed image by a factor of twenty to one. JBIG only defines an Image Compression, not an Image Format. JBIG compressed data is often stored in TIFF files.
JDOM is an API for XML documents. Unlike DOM, which has been designed to be used in a variety of Programming Languages, JDOM has been created specifically for the Java Programming Language. Thus, JDOM has been optimized for Java, and is easier to use than DOM. JDOM is not based on DOM, and it can be used independently from the underlying XML Processor.
JFIF is the technical name for the Image Format better (but inaccurately) known as JPEG. This term is used only when the difference between the Image Format and the Image Compression is crucial. Strictly speaking, however, JPEG does not define an Image Format, and therefore in most cases it would be more precise to speak of JFIF rather than JPEG. Another Image Format for JPEG is SPIFF defined by the JPEG standard itself, but JFIF is much more widespread than SPIFF.
JPEG is the name of the committee that designed the Image Compression algorithm that is also called JPEG.
JPEG is an Image Compression algorithm that is designed for compressing either full-color or grayscale digital images of natural, real-world scenes. It does not work very well on non-realistic images, such as cartoons or line drawings. JPEG does not handle compression of black and white (1 bit per pixel) images or moving pictures. JPEG itself does not describe an Image Format, it only specifies the compression algorithm. Some Image Formats for exchanging images compressed with the JPEG algorithm are the wide-spread JFIF and the less popular SPIFF.
Microsoft's JScript scripting language is a superset of the standardized ECMAScript scripting language. It is mainly intended to be used as a scripting language on HTML pages. Scripts are embedded within WWW pages, and Browsers interpret these scripts after loading the page.
Sun Microsystems's JSP technology uses XML-like tags and scriptlets written in Java to encapsulate the logic that generates the content for a HTML or XML page. Additionally, the application logic can reside in server-based resources that the page accesses with these tags and scriptlets. Any and all formatting tags (HTML or XML) are passed directly back to the response page. This separates the page logic from its design and display, and thereby supports a reusable component-based design. JSP is an extension of the Java servlet API. JSP is Sun Microsystems's proprietary technology to compete with Microsoft's ASP.
The JVM is the "processor architecture" on which Java bytecode (a compiled Java program) is executed. In contrast to other processor architectures, JVM is mostly implemented in software, and available for a large variety of hardware platforms, ranging from mainframe computers to mobile phones and small embedded devices.
L10N is the process of adapting software for a specific region or language by adding locale-specific components and translating text. The abbreviation is based on the fact that the rather lengthy word 'localization' starts with a 'l' followed by 10 characters followed by an 'n'. Usually, the most time-consuming portion of L10N is the translation of text. Other types of data, such as sounds and images, may require L10N if they are culturally sensitive. The formatting of dates, numbers, and currencies also must conform to local requirements. The effort required for the L10N of a system heavily depends on how much I18N has been taken into account when building the system.
LAMP is a concept (or a philosophy) describing an open-source WWW development platform. LAMP is fully based on open-source components, using Linux as its Operating System, the Apache HTTP Server as its HTTP Server, MySQL as its RDBMS, and PHP as its Server Side Technology. Sometimes, the 'P' in LAMP is interpreted as meaning Python or Perl, but in most cases it refers to PHP.
LaTeX is a macro package based on the TeX typesetting system. LaTeX provides macros for the most frequently used document concepts, such as sectioning, lists, or tables.
LDAP was defined in order to encourage adoption of X.500 directories. DAP was regarded as being too complex for simple Internet Clients to use. LDAP defines a relatively simple Protocol for updating and searching directories running over TCP.
LDH form is a Format for host names in the DNS. It constrains valid names to contain only ASCII letters, digits, and hyphens.
LDIF is typically used to import and export directory information between LDAP-based directory servers, or to describe a set of changes which are to be applied to a directory. LDIF is also frequently used by Email agents as file format for directory information (such as address books). LDIF is a text-based format which can be easily manipulated using text-based tools (for XML-based applications, DSML is available as an XML-based version for LDAP information).
LZ77 is a data Compression algorithm that builds a dictionary of frequently repeated groups of bit patterns on a per-file basis and represents these frequent patterns as shorter bit patterns (using the dictionary).
LZW is a refinement of the LZ77 algorithm. The LZW algorithm is patented by Unisys Corporation.
A MAC is an authentication tag (also called a checksum) derived by application of an authentication scheme, together with a secret key, to a message. MACs are computed and verified with the same key so they can only be verified by the intended receiver, unlike digital signatures. MACs can be derived from various cryptographic techniques and algorithms, such as SHA, MD5, or DES.
MCF is a proposal authored by Netscape Communications for the definition of WWW Meta Data. The proposal has been used as input for W3C's work on RDF.
The MD2 algorithm takes as input a message of arbitrary length and produces as output a 128-bit "fingerprint" or "message digest" of the input. It is conjectured that it is computationally infeasible to produce two messages having the same message digest, or to produce any message having a given pre-specified target message digest. MD2 is optimized for 8-bit machines and intended for digital signature applications, where a large file must be "compressed" in a secure manner before being encrypted with a private key under a Public-Key Cryptography system such as RSA.
The MD4 algorithm takes as input a message of arbitrary length and produces as output a 128-bit "fingerprint" or "message digest" of the input. It is conjectured that it is computationally infeasible to produce two messages having the same message digest, or to produce any message having a given pre-specified target message digest. MD4 is aimed at 32-bit machines and intended for digital signature applications, where a large file must be "compressed" in a secure manner before being encrypted with a private key under a Public-Key Cryptography system such as RSA.
The MD5 algorithm takes as input a message of arbitrary length and produces as output a 128-bit "fingerprint" or "message digest" of the input. It is conjectured that it is computationally infeasible to produce two messages having the same message digest, or to produce any message having a given pre-specified target message digest. MD5 is aimed at 32-bit machines and intended for digital signature applications, where a large file must be "compressed" in a secure manner before being encrypted with a private key under a Public-Key Cryptography system such as RSA.
MIDI enables people to use multimedia computers and electronic musical instruments. There are actually three components to MIDI, the communications "Protocol", the Hardware Interface and a distribution format called "Standard MIDI Files". In the context of the WWW, the most interesting component is the Audio Format. In principle, MIDI files contain sequences of MIDI Protocol messages. However, when MIDI Protocol messages are stored in MIDI files, the events are also time-stamped for playback in the proper sequence. Music delivered by MIDI files is the most common use of MIDI today.
MIME provide facilities to allow multiple objects in a single Internet Email message, to represent body text in character sets other than ASCII, to represent formatted multi-font text messages, to represent non-textual material such as images and audio fragments, and generally to facilitate later extensions defining new types of Internet Email for use by cooperating email agents.
A Modem converts digital signals into analog signals which can be transmitted over an analog line (in many cases a PSTN connection), and transforms incoming analog signals into their digital equivalents. The specific technique used to encode the digital bits into analog signals is called "Modulation Protocol", which defines the exact method of encoding and the data transfer speed. A Modem typically supports more than one Modulation Protocol.
MOSS is a Protocol that uses the MIME multipart/signed and multipart/encrypted framework to apply digital signature and encryption services to MIME objects. The services are offered through the use of end-to-end cryptography between an originator and a recipient at the application layer. Public-Key Cryptography is used in support of the digital signature service and encryption key management. Secret-Key Cryptography is used in support of the encryption service. The procedures are intended to be compatible with a wide range of public key management approaches, including both ad hoc and certificate-based schemes. Mechanisms are provided to support many public key management approaches.
In March 1998, Netscape Communications decided that the Communicator product (including the Navigator Browser) would be available free of charge, and that the source code would also be available free of charge. The idea behind this decision is to encourage the public to take part in the development of Navigator (which has the nickname of Mozilla). Hopefully, this will result in more functionality and availability for more platforms than could be provided by Netscape Communications alone. The Mozilla organization is hosted by Netscape Communications and tries to coordinate the efforts by managing the source code and maintaining a list of what should be implemented in the future.
NITF uses XML to define the structure and content of news articles (text and statistical data). It identifies structural pieces such headlines, bylines, paragraphs, table columns and footnotes. The subjects covered by the content may be indicated through the use of IPTC subject codes. Rich in-line markup can be applied to specify such things as organizations, events, places and people. Because metadata tags are applied throughout the news content, NITF documents are more searchable and useful than HTMLpages. NITF documents, like other news data may be contained within, or referenced from, a NewsML wrapper.
NNTP specifies a protocol for the distribution, inquiry, retrieval, and posting of Usenet News articles using a reliable stream-based transmission of Usenet News among the Internet community. NNTP is designed so that Usenet News articles are stored in a central database allowing a subscriber to select only those items he wishes to read. Indexing, cross-referencing, and expiration of aged messages are also provided.
A Nonce is a randomly generated value used to defeat "playback" attacks in communication Protocols. One party randomly generates a nonce and sends it to the other party. The receiver encrypts it using the agreed upon secret key and returns it to the sender. Since the nonce was randomly generated by the sender, this defeats playback attacks because the replayer can not know in advance the nonce the sender will generate. The receiver denies connections that do not have the correctly encrypted nonce.
NTP provides the mechanisms to synchronize time and coordinate time distribution in a large, diverse Internet operating at rates from mundane to light-wave. It uses a returnable-time design in which a distributed subnet of time Servers operating in a self-organizing, hierarchical-master-slave configuration synchronizes local clocks within the subnet and to national time standards via wire or radio. The Servers can also redistribute reference time via local routing algorithms and time Servers. A simpler variant of NTP has been specified under the name of SNTP.
A NUN is a name that uniquely identifies an element, attribute, simple type, complex type, attribute group, model group, or notation declaration in an XML Schema.
OASIS is a nonprofit, international Consortium dedicated to accelerating the adoption of product-independent formats based on public standards. These standards include SGML, XML, and HTML as well as others that are related to structured information processing. Members of OASIS are providers, users, and specialists of the technologies that make these standards work in practice.
OLE is a compound document standard developed by Microsoft. OLE makes it possible to create objects with one application and link or embed them in a second application. Embedded objects retain their original format and links to the application that created them. Support for OLE is built into the Windows and MacOS Operating Systems. A competing compound document standard developed mainly by Apple and IBM is called OpenDoc.
Established in 1989, OMG promotes the theory and practice of object technology for the development of distributed computing systems. The goal is to provide a common architectural framework for object oriented applications based on widely available interface specifications. OMG has a membership of over 800 software vendors, software developers, and end users. CORBA is standardized by the OMG.
OpenDoc is an open, multi-platform architecture for component software developed mainly by Apple and IBM. It is a Component Model as well as an API that makes it possible to design independent programs (components) that can work together on a single document. In favor of Java technology, Apple announced its plans to reduce its investment in OpenDoc technologies. The competing product to OpenDoc is Microsoft's OLE.
The OpenType Font Format is an extension of the TrueType Font Format, adding support for Type 1 font data. The OpenType Font Format was developed jointly by Microsoft and Adobe. As with TrueType fonts, OpenType fonts allow the handling of large glyph sets using Unicode encoding. Such encoding allows broad international support, as well as support for typographic glyph variants. Additionally, OpenType fonts may contain digital signatures, allowing Operating Systems and Browsers to identify the source and integrity of font files, including embedded font files obtained in WWW documents, before using them. Also, font developers can encode embedding restrictions in OpenType fonts, and these restrictions cannot be altered in a font signed by the developer.
The ORB is the key component of the CORBA programming model. An ORB is responsible for transferring operations from Clients to Servers. This requires the ORB to locate a Server implementation (and possibly activate it), transmit the operation and its parameters, and finally return the results back to the Client.
OSI is a reference model for computer communications. It was created as a competitor of the Internet Protocols. While OSI as a whole has not been very successful, parts of it are widely used, and many concepts pioneered in OSI are slowly finding their way into Internet technologies. OSI is defined in terms of different "layers". OSI-based applications belong to the "application layer" (layer 7) of the OSI "Basic Reference Model". The application layer resides above the "presentation layer" (layer 6), which identifies alternative encodings, and the "session layer" (layer 5), providing dialogue control. Collectively, these three layers provide application services, and are commonly referred to as the "upper layers". The "lower layers" of the OSI stack are "transport" (layer 4), "network" (layer 3), "link" (layer 2) and "physical" (layer 1).
P2P networking is a network model where, depending on an operation's context, any node can operate as either a Server or a Client. P2P provides certain interesting capabilities not possible in traditional Client/Server-Model networks, which have predefined Server or Client roles for their nodes.
The goal of P3P is to deal with the constant struggle between the need for WWW content providers to gain information about their readership and the need for these individuals to control the release of this information to others. P3P addresses the twin goals of meeting the data privacy expectations of consumers on the WWW while assuring that the medium remains available and productive for E-Commerce. Following the principle of providing consumers notice of site privacy polices, and allowing users to express and act upon their privacy preferences in a flexible manner, one goal enhances the success of the other.
PCT was designed by Microsoft in an attempt to improve Netscape Communications's SSL protocol. However, development of PCT stopped when SSL was generalized as IETF's TLS protocol.
PDF is a Format for representing documents in a manner that is independent of the original application software, hardware, and operating system used to create those documents. A PDF file can describe documents containing any combination of text, graphics, and images in a device-independent and resolution independent format. The advantage of PDF over PostScript is the better accessibility of text within PDF files, which can still be searched for text and can also contain structural information like a table of contents.
PDFLaTeX is a special version of LaTeX which directly produces PDF output. Special commands in the LaTeX source can be used to control special PDF features, such as cross references or bookmarks.
PDF/X is not an alternative to PDF, it is a focused subset of PDF designed specifically for reliable prepress data interchange.
PDOM is a Concept rather than a specific API or Format. While DOM defines a standardized API for accessing XML documents, PDOM is a concept for storing the in-memory information of the DOM tree on a persistent Storage Medium. Typically, PDOM implementations use a binary and indexed Format, and provide a DOM-like API, which can be used to access this Format. However, the specific Format used for PDOM varies and has not been standardized.
Perl is a general purpose interpreted Programming Language, often used for scanning text and printing formatted reports. It provides extensive support for Regular Expression matching, dynamically scoped variables and functions, extensible run-time libraries, exception handling, and packages. Perl is frequently used for programming CGI applications.
PGML is a 2D Graphics Format meant to satisfy both the WWW's scalable lightweight vector graphics needs and the precision needs of graphic artists who want to ensure that their graphic designs appear on end user systems with precisely the correct fonts, color, layout and compositing that they desire. Graphics Format uses the imaging model of PostScript. PGML was a proposal authored by Adobe and has been used as input for the development of SVG.
PHP is an HTML-embedded scripting language. Much of its syntax is borrowed from C, Java, and Perl, with the addition of a couple of unique PHP-specific features. The goal of the language is to allow WWW developers to write dynamically generated HTML pages quickly. PHP is either executed as a CGI script, or it is integrated into HTTP Server software, for example as an Apache HTTP Server module.
PICS is a pair of Protocols, allowing labels to be applied to WWW content. These Protocols empower any individual or organization to design and distribute labels reflecting their views about the content. PICS was pioneered by W3C as a practical alternative to global governmental censorship of the Internet. In addition, the same technology facilitates searching the WWW and provides a foundation for establishing trust in information on the WWW. PICS labels are rather limited in their expressiveness. A new version of PICS will be based on RDF, facilitating more complex labeling of resources.
PIP enables the exchange of document based virtual presence information. Virtual presence information is the foundation for virtual neighborhood services which provide users with information about virtual neighbors, ie other users who are close within the virtual document space established by the WWW. PIP also allows the exchange of simple text-based messages.
PKCS are specifications produced by RSA Laboratories in cooperation with secure systems developers worldwide for the purpose of accelerating the deployment of Public-Key Cryptography. First published in 1991 as a result of meetings with a small group of early adopters of Public-Key Cryptography technology, the PKCS documents have become widely referenced and implemented. The PKCS standards cover RSA encryption, Diffie-Hellman key agreement, password-based encryption, extended-certificate syntax, CMS, private key information syntax, and certification request syntax, as well as selected attributes. Contributions from the PKCS series have become part of many formal and de facto standards, including PKIX, SET, S/MIME, and SSL.
POP allows a Client computer to retrieve Email from a POP Server. It does not provide for sending Email, which is assumed to be done via SMTP or some other method. POP is useful for computers without a permanent Network connection which therefore require a "post office" (the POP Server) to hold their Email until they can retrieve it. POP is older and less powerful than the IMAP, which is used for the same application area.
While IP makes it possible for two systems to exchange datagrams in a heterogeneous network environment, it does not support the identification of different processes on these systems. TCP and UDP as the transport Protocols of the Internet thus introduce the concept of a Port, which addresses a specific process on a system. Port numbers are 16-bit numbers, which are included in TCP or UDP packets and are used to address a specific process on a system.
PostScript is an interpreted, stack-based Programming Language. Its primary application is to describe the appearance of text, graphics, and images on printed or displayed pages. A program in PostScript can communicate a document description from a composition system to a printing system in a device-independent way. PostScript is an unusually powerful printer language because it is a full programming language, rather than a series of low-level escape sequences. The latest version of PostScript, version 3, fully integrates PDF.
PPP is designed for simple links which transport packets between two peers. These links provide full-duplex simultaneous bi-directional operation, and are assumed to deliver packets in order. Although PPP is not tied to a particular type of packets it transports, its most common use is the encapsulation of IP packages over Modem lines. Basically, PPP is similar to SLIP, but it has the advantages of not being limited to one type of Protocol it can transport, a configuration negotiation phase at the start of a connection (for determining connection configuration parameters automatically), and the possibility to use standardized authentication procedures for automated login. The two authentication schemes supported by PPP are PAP and CHAP.
A Proxy is a special kind of Gateway, acting like a Server when being accessed by a Client. However, instead of servicing a request from a Client, the Proxy forwards the request to a Server, waits for the Server's response, and then sends it back to the Client. A Proxy is often combined with other typical Gateway functionality, such as Firewall or Cache.
PSTN refers to the established international telephone system carrying voice data over circuit switched connections. Newer developments such as ISDN are completely digital, while PSTN traditionally works on an analog basis (even though PSTN-based networks also increasingly are implemented using digital technologies).
Python is an interpreted, interactive, object-oriented Programming Language. The language has a concise syntax; a small number of powerful high-level data types are built in. Python can be extended in a systematic fashion by adding new modules implemented in a compiled Programming Language such as C or C++. Such extension modules can define new functions and variables as well as new object types. Python is frequently used for programming CGI applications.
QuickTime is Apple's architecture for handling multimedia data. First versions of QuickTime were basically a Format for audio and video, newer versions integrate streaming capabilities as well as more media types, including support for 3D and virtual reality. Being a proprietary technology, QuickTime can be compared to Microsoft's ASF.
A Display Standard referring to a video adapter capable of a resolution of up to 2048 by 1536 pixels.
RDF is designed to provide an infrastructure supporting Meta Data across many WWW-based activities. RDF is the result of a number of Meta Data communities bringing together their needs to provide a robust and flexible architecture for supporting Meta Data on the Internet and the WWW. Example applications include site maps, content ratings, stream channel definitions, search engine data collection, digital library collections, and distributed authoring. RDF allows different application communities to define the Meta Data property set that best serves the needs of each community. RDF provides a uniform and interoperable means to exchange the Meta Data between programs and across the WWW. Furthermore, RDF provides a means for publishing both a human-readable and a machine-understandable definition of the property set itself. RDF uses XML as the transfer syntax in order to leverage other tools and code bases being built around XML.
A Repeater is a device that connects networks segments on the physical layer of the network. Related to Repeaters are Bridges, Routers, and Gateways, which also connect network segments, but on different layers of the networking architecture.
RFCs form a series of publications of networking technical documents, started in 1969 as part of the original ARPA wide-area networking (ARPANET) project. RFCs cover a wide range of topics, from early discussion of new research concepts to status memos about the Internet. The IAB views the RFC publication process to be sufficiently important to warrant including the RFC editor in the IAB membership. The status of specifications on the Internet standards track is summarized periodically in a summary RFC entitled "Internet Official Protocol Standards". This RFC shows the level of maturity and other helpful information for each Internet Protocol or service specification. The "Internet Official Protocol Standards" RFC is the authoritative statement of the status of any particular Internet specification, and it is the "Publication of Record" with respect to Internet standardization.
RMI is an RPC mechanism enabling Java programmers to create distributed applications, in which the methods of remote Java objects can be invoked from another JVM, possibly on a different host. A Java program can make a call on a remote object once it obtains a reference to the remote object, either by looking up the remote object in the bootstrap naming service provided by RMI, or by receiving the reference as an argument or a return value. A Client can call a remote object in a Server, and that Server can also be a Client of other remote objects. RMI uses object serialization to marshal and unmarshal parameters and does not truncate types, supporting true object-oriented polymorphism.
A Router is a device that connects networks segments on the network layer of the network. Related to Routers are Repeaters, Bridges, and Gateways, which also connect network segments, but on different layers of the networking architecture.
RSA is a Public-Key Cryptography system for both encryption and authentication (its name is derived from the surnames of the three inventors). For encryption, RSA is combined with a Secret-Key Cryptography system, such as DES, to encrypt a message by means of an RSA digital envelope. For authentication, RSA is usually combined with a Cryptographic Hash Function, such as MD5, to sign a message.
RTCP is the control Protocol that works in conjunction with RTP. RTCP control packets are periodically transmitted by each participant in an RTP session to all other participants. Feedback of information to the application can be used to control performance and for diagnostic purposes.
RTP provides end-to-end network transport functions suitable for applications transmitting real-time data, such as audio, video, or simulation data, over multicast or unicast network services. RTP does not address resource reservation and does not guarantee quality-of-service for real-time services. The data transport is augmented by a control protocol (RTCP) to allow monitoring of the data delivery in a manner scalable to large multicast networks, and to provide minimal control and identification functionality. RTP and RTCP are designed to be independent of the underlying transport and network layers.
RTSP is an application-level Protocol for control over the delivery of data with real-time properties. RTSP provides an extensible framework to enable controlled, on-demand delivery of real-time data, such as audio and video. Sources of data can include both live data feeds and stored clips. RTSP is intended to control multiple data delivery sessions, provide a means for choosing delivery channels such as UDP, multicast UDP and TCP, and use delivery mechanisms based upon RTP.
SAX is a standard API for event-based XML parsing, and SAX implementations are available in different programming languages. SAX is the event-based alternative to the tree-based DOM, which also provides an API for accessing XML documents. An event-based API reports parsing events (such as the start and end of elements) directly to the application through callbacks, and does not usually build an internal tree. The application implements handlers to deal with the different events. The advantage of this approach is simpler processing, in particular the ability to process XML documents without the need to keep them in memory, which makes it possible to process XML documents that exceed the capacity of memory available for processing.
SET is an industry-wide Protocol designed to safely transmit sensitive personal and financial information over public Networks. SET contains state-of-the-art cryptographic technology that provides online transaction security that is equivalent or superior to the safeguards in present physical, Email, and telephone card transactions. PKCS is the set of Public-Key Cryptography algorithms used in SET. The Secret-Key Cryptography algorithm is DES.
SGML is a markup language for structured documents. Being the foundation for HTML, SGML today is the most frequently used language for structuring documents. The rules for how documents of a certain type may be structured are specified in a DTD, and every application of SGML (such as HTML) defines such a DTD. Even though SGML has been very successful, it is also rather complex and contains a lot of obscure features which are rarely used (and implemented). Thus, when a new language for replacing HTML on the WWW was needed, rather than directly taking SGML, a functional subset of SGML was defined, which has become known under the name of XML.
SHOE is an XML-based knowledge representation language, a superset of HTML which adds the tags necessary to embed arbitrary semantic data into WWW pages. SHOE tags are divided into two categories. First, there are tags for constructing ontologies. SHOE ontologies are sets of rules which define what kinds of assertions SHOE documents can make and what these assertions mean. Secondly, there are tags for annotating SHOE documents to subscribe to one or more ontologies, declare data entities, and make assertions about those entities under the rules prescribed by the ontologies.
S-HTTP is an extension of HTTP providing independently applicable security services for transaction confidentiality, authenticity/integrity and non-repudiability of origin. The protocol emphasizes maximum flexibility in choice of key management mechanisms, security policies and cryptographic algorithms by supporting option negotiation between parties for each transaction. Message protection can be provided on three orthogonal axes: signature, authentication, and encryption. Any message may be signed, authenticated, encrypted, or any combination of these (including no protection). Several cryptographic message format standards may be incorporated into S-HTTP clients and servers, particularly, but in principle not limited to, PKCS-7 and PEM. S-HTTP-aware clients can communicate with S-HTTP-oblivious servers and vice-versa. Cryptographic algorithms supported by S-HTTP include DES, two-key and three-key 3DES, DESX, IDEA, RC2, and CDMF.
SLIP is a packet framing Protocol, it defines a sequence of characters that frame IP packets on a serial line. It provides no addressing, packet type identification, error detection/correction, or compression mechanisms. It is used for the same purpose as PPP, which is the encapsulation of IP packages over Modem lines. SLIP does not have PPP's configuration negotiation or authentication schemes, which can make the configuration of SLIP connections more complicated.
The GSM SMS is a very simple service for transmitting short messages (140 octets of user data) over the GSM network. It has become a very popular service for mobile phone users. The EMS and MMS technologies have been designed to become the predecessors of SMS.
SMTP is used to pass Email messages between Internet Servers. Each message has a standardized header that is used to identify Email address(es) of the person(s) the message is to be sent to, the Email address and name of the sender (to whom responses can be sent automatically), and details of those nodes on the network through which the message passed. A number of extensions to SMTP have been defined yielding ESMTP, which is mostly in use today.
SPEC was founded in 1988 by a small number of workstation vendors. SPEC has grown to become one of the more successful performance standardization bodies with more than 40 member companies. SPEC publishes several hundred different performance results each quarter spanning across a variety of system performance disciplines. The goal of SPEC is to ensure that the marketplace has a fair and useful set of metrics to differentiate candidate systems. The path chosen is an attempt to balance between requiring strict compliance and allowing vendors to demonstrate their advantages.
SPECweb a standardized benchmark for comparing HTTP Server performance. The benchmark is designed to provide comparable measures of how well systems can handle HTTP GET requests. The workload s based upon analysis of HTTP Server logs from WWW sites ranging from a small personal server up through some of the WWW's most popular servers.
SPIFF is the "official" Image Format for images using the JPEG Image Compression algorithm. Part 3 of the JPEG standard includes a fully defined Image Format for storing JPEG data. When the JPEG format was first standardized, disagreements among ISO committees prevented a standard JPEG Image Format from being created. The de-facto format that appeared was JFIF from C-cube Microsystems. The JFIF Image Format, although now widespread, is very limited in capability as Image Formats go. SPIFF is intended to replace JFIF, adding features (more color spaces, a recognized way of including text blocks, and so forth), and providing a backwards-compatibility allowing SPIFF files to be read by most JPEG/JFIF decoders. JFIF, however, has a five-year head start on SPIFF, so the likelihood of it being completely replaced anytime soon is not good.
The aim of the sRGB Color Space is to complement the current color management strategies by enabling a third method of handling color in Operating Systems, device drivers and the Internet that utilizes a simple and robust device independent color definition. This will provide good quality and backward compatibility with minimum transmission and system overhead. Based on a calibrated colorimetric RGB color space well suited to CRT monitors, television, scanners, digital cameras, and printing systems, such a space can be supported with minimum cost to software and hardware vendors.
SSI make it possible to include information into WWW pages before delivering them to a HTTP Client. A WWW page using SSI contains special instructions which are interpreted by the HTTP Server whenever the WWW page is requested. These instructions may specify to include other documents (eg, document headers or footers) or to insert dynamic information, such as the current date or an access count. There is no standard for SSI, so each HTTP Server implementation uses its own syntax and functionality.
The primary goal of SSL is to provide privacy and reliability between two communicating applications. SSL is composed of two layers. At the lower level, layered on top of some reliable transport Protocol, for example TCP, is the SSL Record Protocol, which is used for encapsulation of various higher level protocols. One such encapsulated protocol, the SSL Handshake Protocol, allows the server and client to authenticate each other and to negotiate an encryption algorithm and cryptographic keys before the application protocol transmits or receives its first byte of data. One advantage of SSL is that it is application Protocol independent. A higher level Protocol can layer on top of SSL transparently. For Internet applications, a generalized variant of SSL called TLS has been developed.
SVG is a language for describing two-dimensional graphics in XML. SVG allows for three types of graphic objects: vector graphic shapes (eg, paths consisting of straight lines and curves), images, and text. Graphical objects can be grouped, styled, transformed and composited into previously rendered objects. Text can be in any of the XML Namespaces suitable to the application, which enhances searchability and accessibility of the SVG graphics. The feature set includes nested transformations, clipping paths, alpha masks, filter effects, template objects and extensibility. SVG drawings can be dynamic and interactive. DOM for SVG, which includes the full XML DOM, allows for straightforward and efficient vector graphics animation via scripting. Event handlers can be assigned to any SVG graphical object. Because of its compatibility and leveraging of other WWW standards, features like scripting can be done on SVG elements and other XML elements from different XML Namespaces simultaneously within the same WWW page.
A Display Standard referring to a video adapter capable of a resolution of up to 800 by 600 pixels.
A Display Standard referring to a video adapter capable of a resolution of up to 1280 by 1024 pixels.
A Display Standard referring to a video adapter capable of a resolution of up to 1400 by 1050 pixels.
T9 is a technology for rapidly typing alphanumeric text on a numeric keypad. It is based on a dictionary and thus language-dependent. T9 is often used on mobile phones to facilitate text input for messaging, for example for composing SMS messages.
Tcl is a general-purpose, robust Programming Language that can easily be integrated into new applications. One of Tcl's most useful features is its extensibility. If an application requires some functionality not offered by standard Tcl, new Tcl commands can be implemented using the C language, and integrated fairly easily. Since Tcl is so easy to extend, many people have written extension packages for common tasks, and made these freely available. Tcl is frequently used for programming CGI applications.
TCP is intended for use as a highly reliable transport Protocol between hosts in packet-switched computer communication Networks, and in interconnected systems of such Networks. TCP is a flow-controlled, connection-oriented, end-to-end reliable Protocol designed to fit into a layered hierarchy of Protocols supporting multi-network applications. TCP provides for reliable interprocess communications between pairs of processes in host computers attached to distinct but interconnected computer communication Networks. Very few assumptions are made as to the reliability of the communication Protocols below the TCP layer. TCP assumes it can obtain a simple, potentially unreliable, datagram service from the lower level Protocols, usually IP. TCP is able to operate above a wide spectrum of communication systems, ranging from hard-wired connections to packet-switched or circuit-switched networks.
The purpose of the Telnet Protocol is to provide a fairly general, bi-directional, 8-bit byte oriented communications facility. Its primary goal is to allow a standard method of interfacing terminal devices and terminal-oriented processes to each other. The most popular usage of Telnet is for logging in into remote systems. In this scenario, the Telnet Client is the remote terminal (usually running some kind of terminal emulation) which is connected to a terminal driver program using the Telnet Protocol.
TeX is a typesetting system for high-quality document preparation. TeX itself does not provide a GUI like most word processing programs, but is invoked to process a document which contains commands and the actual content. Because of its superior formatting of mathematical formulae, TeX is very popular in the scientific community. TeX is most often used in the form of LaTeX, which is a macro package based on TeX. Another popular tool in the context of TeX is BibTeX, a program for processing bibliographic databases.
THX defines a set of guidelines for audio and picture playback for movie theatres. Often confused with Movie Sound Formats, THX does not define standards for audio coding, it only defines the presentation standards that must be met during movie playback. Any Movie Sound Format may be used, as long as it provides the standards set by THX.
TIFF defines a tag-based Image Format that can characterize almost any form of 2D raster data using either ASCII or binary coding. "Private" tags may be used to allow additional parameters to be added to the descriptor. "Standard" TIFF allows the use of PackBits, LZW, G3 Fax, G4 Fax, and JPEG compression schemes within transmitted images. Four photometric classes are supported: TIFF-B for monochrome, TIFF-G for grayscale, TIFF-P for palette-based coding, and TIFF-R for RGB coding.
A TLD is that part of a DNS FQDN which stands right of the rightmost full stop. Two letter TLDs designate ccTLDs, and three letter TLDs designate gTLDs.
TLS was developed as the successor to SSL, and is nearly identical to SSL, except that it implements an open and standards-based solution, more non-proprietary ciphers, better error reporting, and HMAC digests instead of simple MD5. The structure of the start of a TLS session allows negotiation of the level of the protocol to be used. This way, a Client or Server can simultaneously support TLS and SSL and negotiate the most appropriate protocol for the connection.
Topic Maps enable vast information resources (such as the WWW) to be classified and navigated in a consistent manner. They allow for the concepts or topics that underlie a set of information resources to be exposed to those people or applications processing the information. Information resources can be HTML, PDF, XML, SGML and other Formats including paper. Topics are the concepts underlying what these resources are concerned with. A topic can reference zero or more information resources. In addition to grouping resources as "topic occurrences", it is possible to have meta level associations. This means that it is possible to define a link, or association, from one topic to another. Topic Maps provide a semantic layer that is not hierarchical, although it could be visualized that way, it facilitates navigation at a level independent from the information resources.
TrAX is an API for transforming XML documents using XSLT style sheets. TrAX is a Java API and has been defined to provide common access to different XSLT Processors. TrAX is part of the JAXP API, which combines a number of Java APIs.
TrueType is a Font Format developed by Apple and licensed to Microsoft. TrueType is the native Operating System Font Format for Windows and MacOS. TrueType contains a hierarchical set of tables and glyph representations. Characters can be hinted on a per character and point size basis yielding excellent quality at screen resolutions. TrueType fonts for Windows and MacOS have few differences, though they can be different enough to prevent cross platform usage. Font foundries provide TrueType fonts for each platform and usually include a license preventing electronic manipulation to achieve cross platform transparency. TrueType is one of the foundations for the OpenType Font Format.
Originally developed by Adobe for their PostScript page description language, the Type 1 Font Format has been accepted as an ISO standard. Type 1 fonts use a specialized subset of the PostScript language which is optimized for better performance and a more compact representation. The Type 1 operator set includes hint information which helps font rasterizers create more accurate bitmaps for smaller sizes and lower resolutions. Type 1 is one of the foundations for the OpenType Font Format.
UCS standardized in ISO 10646 integrates all previous internationally/nationally agreed character sets into a single code set. UCS is based on 4-octet (32-bit) coding scheme known as the "canonical form" (UCS-4), but a 2-octet (16-bit) form (UCS-2) is used for the BMP, where octets 1 and 2 are assumed to be 00 00. The code set is split into 128 "groups" of "planes" containing 256 "rows" with 256 "cells" for characters. Each character is addressed using multiple octets, the third (in UCS-2 the first) of which identifies the row containing the character and the fourth (in UCS-2 the second) its cell number. The first 127 characters of the BMP used for 16-bit code interchange are those of ASCII. The characters forming the second half of the first row are those used in ISO 8859-1, the Latin-1 character set.
UDDI provides a standardized method for publishing and discovering information about Web services. UDDI is an industry initiative that attempts to create a platform-independent, open framework for describing services, discovering businesses, and integrating business services. UDDI focuses on the process of discovery in the service-oriented architecture (WSDL is often used for service description, and SOAP for service invocation). Being a Web service itself, UDDI is invoked using SOAP. In addition, UDDI also defines how to operate servers and how to manage replication among several servers.
UDP is a transport Protocol that provides a simple but unreliable datagram service. UDP neither guarantees delivery nor does it require a connection. As a result, it is lightweight and efficient, but all error processing and retransmission must be taken care of by the application program. Like TCP, which is the Internet's other important transport Protocol, UDP is layered on top of IP.
UNC provides a naming convention for identifying network resources. UNC identifiers consist of three parts, a server name, a share name, and an optional file path, that are combined using backslashes or slashes. UNC notation is used primarily for mapping network drives in the Windows family of Operating Systems, although support for UNC appears in related technologies like SMB/CIFS. UNC names are most commonly used to reach file servers or printers on a LAN.
Unicode defines a 31-bit character set. Unicode is closely aligned with UCS. The most commonly used characters, including all those found in older encoding standards, have been placed in one of the first 65534 positions (0x0000 to 0xFFFD). This 16-bit subset is called the BMP or "Plane 0". The characters that were later added outside the 16-bit BMP are mostly for specialist applications such as historic scripts and scientific notation. New characters are still being added on a continuous basis, but the existing characters will not be changed any more and are stable. Unicode assigns to each character not only a code number but also an official name. A hexadecimal number that represents a Unicode or UCS value is commonly preceded by "U+" as in U+0041 for the character "Latin capital letter A". The Unicode characters U+0000 to U+007F are identical to those in ASCII, and the range U+0000 to U+00FF is identical to ISO 8859-1 (Latin-1).
The WWW is considered to include objects accessed using an extendable number of Protocols, existing, invented for the WWW itself, or to be invented in the future. Access instructions for an individual object under a given Protocol are encoded into forms of address string. Other Protocols allow the use of object names of various forms. In order to abstract the idea of a generic object, the WWW needs the concepts of the universal set of objects, and of the universal set of names or addresses of objects. A URI is a member of this universal set of names in registered name spaces and addresses referring to registered Protocols or name spaces. A URL is a form of URI which expresses an address mapping onto an access algorithm using network Protocols. A URN is a form of URI which uses a name space (and associated Resolution Protocols) for persistent object names.
A URL is the address of a resource which is retrievable using Protocols already deployed on the Internet. A URL defines an access Protocol, called a "scheme", and a "scheme-dependent part", which has to provide sufficient information to locate an object using the specified scheme. In case of HTTP URLs, the scheme is "http", and the scheme-dependent part specifies the name of the HTTP Server as well as the path of the object on the HTTP Server.
A URN is a persistent, globally unique name assigned to an object. In contrast to a URL, which changes whenever the location of an object changes, a URN has no location dependence and therefore a longer lifetime. This is realized by using a naming service which in most cases will provide a mapping from URNs to URLs. Thus, even if the URL of an object changes, its URN remains the same, since only the object's entry in the naming service has to be updated.
Usenet News can be regarded as the oldest Internet application for global distribution of information. It originated in 1979 at the University of North Carolina. It is simply a set of machines (Usenet News Servers) which cooperate to exchange (using NNTP) articles tagged with one or more labels, which are called "newsgroups". Newsgroups are organized hierarchically according to the subjects of the articles belonging to them. Newsgroups or individual articles in newsgroups can be addressed using a special URL scheme.
UTF is used for coding UCS characters. Although UCS defines character codings (UCS-2 and UCS-4), they are hard to use in many current applications and protocols that assume 8- or even 7-bit characters. UTF formats usually are variable length formats, for example in UTF-8 a character is represented by 1 to 6 bytes, while in UTF-16 a character is represented by 2 to 4 bytes (UTF-32, however, always encodes characters as 4 bytes).
UTF-32 is the UTF that serializes a Unicode code point as a sequence of four bytes, in either big-endian (UTF-32BE) or little-endian UTF-32LE format. An initial sequence corresponding to U+FEFF is interpreted as a BOM, it is used to distinguish between the two byte orders. The BOM is not considered part of the content of the text. A serialization of Unicode code points into UTF-32 may or may not begin with a BOM The term UTF-32 can be used ambiguously. When referring to the encoding of Unicode in memory, there is no associated byte orientation, and a BOM is never used. When referring to a serialization of Unicode code points into bytes, it may have a BOM and either byte orientation..
A Display Standard referring to a video adapter capable of a resolution of up to 1600 by 1200 pixels.
Microsoft's VBScript is a subset of the Microsoft Visual Basic Programming Language. VBScript is a portable, lightweight interpreter for use in Browsers and other applications that use ActiveX controls.
A Display Standard referring to a video adapter capable of a resolution of up to 640 by 480 pixels.
A VPN is a private Network that makes use of the public telecommunication infrastructure, maintaining privacy through the use of a tunneling Protocol and security procedures. A VPN can be contrasted with a system of owned or leased lines that can only be used by one company. The main purpose of a VPN is to give the company the same capabilities as private leased lines at much lower cost by using the shared public infrastructure.
VRML is a Format for 3D multimedia and shared virtual worlds on the WWW. In comparison to HTML, VRML adds the next level of interaction, structured graphics, and extra dimensions (z and time) to the presentation of documents. The applications of VRML are broad, ranging from simple business graphics to entertaining WWW page graphics, manufacturing, scientific, entertainment, and educational applications, and 3D shared virtual worlds and communities.
Founded in 1994 to develop common Protocols for the evolution of the WWW, W3C is an international association of industrial and service companies, research laboratories, educational institutions, and organizations of all sizes. All of these organizations share a compelling interest in the long term evolution and stability of the WWW. W3C is a non-profit organization funded partly by commercial members. Its activities remain vendor neutral, however. W3C also receives the support of governments who consider the WWW the platform of choice for a global information infrastructure.
WAE is the uppermost layer in the WAP software stack, this layer provides basic components on which ASPs can develop their mobile applications.
WAIS is designed to help users find information over a computer network. The WAIS software architecture has four main components: the Client, the Server, the database, and the Protocol. The WAIS Client is a UI that sends requests for information to local or remote Servers. The WAIS Server is a program that services Client requests. The Server generally runs on a machine containing one or more information sources, or WAIS databases. The Protocol, Z39.50-1988, is used to connect WAIS Clients and Servers and is based on the 1988 version of the NISO Z39.50 standard. Since the WWW allows greater flexibility in the structure and presentation of distributed information, the usage of WAIS services and the number of WAIS Servers is getting smaller.
WAP enables mobile users with wireless devices to easily access and interact with information services. WAP is not a single standard for data communications or document formats, but a whole suite of specifications ranging from data transport Protocols to the WML, which is a markup language similar to HTML, but based on XML and specifically designed for wireless devices. There are five layers to the WAP stack: the application layer (WAE), the session layer (WSP), the transaction layer (WTP), the security layer (WTLS), and the transport layer (WDP).
WAVE is a proprietary standard for audio files developed by Microsoft. The format can store monaural or multichannel sampled sounds in a range of sampling types, sample rates and sample resolutions.
WBXML is a binary format for WML, the Hypertext Format of WAP. WBXML may either be delivered by the origin server itself, or the origin server delivers WML, and the WAP Gateway performs the transformation between WML and WBXML. WBXML works by defining a tokenization method for WML, where each element and each attribute is represented by a compact binary token.
WebCGM is a profile of the ISO CGM standard, tailored to the requirements for scalable 2D vector graphics in electronic documents on the WWW. The WebCGM profile is a subset of the CGM standard, and a set of specifications targeted especially at the effective application of the CGM standard to representation of 2D graphical content within WWW documents.
WebDAV defines extensions to HTTP to enable distributed WWW authoring tools to be broadly interoperable. HTTP already contains functionality which enables the editing of WWW content at a remote location, without direct access to the storage media via an Operating System. This capability is exploited by several existing HTML distributed authoring tools, and by a growing number of mainstream applications (eg, word processors) which allow users to write (publish) their work to an HTTP Server. Experience from the HTML authoring tools has shown they are unable to meet their user's needs using the facilities of HTTP. The consequence of this is either postponed introduction of distributed authoring capability, or the addition of nonstandard extensions to HTTP. These extensions, developed in isolation, are not interoperable.
The WebFonts specification is part of CSS2, it allows improved client-side font matching, enables font synthesis and progressive rendering, and enables fonts to be downloaded over the WWW. However, WebFonts does not specify a particular data format for downloadable fonts, it only defines a mechanism for font description.
The SGML standard has been updated with two annexes which add some corrections as well as new features to SGML making some specifications possible which are desirable for using SGML as the basis for HTML and XML. Basically, the WebSGML extensions allow a number of additional features to be defined in an SGML declaration and DTD. However, when using these features in an SGML environment, it is necessary that both the generator and the interpreter of a document are capable of processing the WebSGML extensions, since a conforming SGML implementation does not have to implement the WebSGML extensions.
WebStone is a benchmark for measuring the performance of HTTP Server platforms (software and hardware combined). It is designed to measure the performance of HTTP Servers under multiple scenarios which reflect different WWW site profiles. The test uses workload parameters and clients to generate HTTP traffic that allows an HTTP Server to be stressed in a number of different ways.
Wi-Fi is a label for devices conforming to the IEEE 802.11b standard for WLAN. The IEEE 802.11b standard has been published by the IEEE, which does not perform conformance testing. In order to establish such a conformance testing process, the WECA has been formed, which tests devices for conformance with the IEEE 802.11b standard and issues the Wi-Fi label for conforming devices.
A WLAN is a LAN that is based on a Wireless Interface. WLAN technology makes using LANs easier, because users can roam within the coverage area of the WLAN without having to deal with cables.
WML is the Hypertext Format for WAP. WML is based on XML (it is formally defined by an XML DTD). WML pages can be stored on any HTTP Server, which will be contacted by a WAP Gateway and deliver the WML page. The WAP Gateway then transforms the WML page into WBXML, which is then transmitted to the WAP device. WML is similar to HTML in its design, and WAP also defines WMLScript which may be used to implement dynamic WML.
WSP forms the interface between WAE and the rest of the WAP stack. WSP operates in two modes, connectionless and connection, supports the transmission of WML, and can be regarded as the binary equivalent of HTTP.
A Display Standard referring to a video adapter capable of a resolution of up to 1680 by 1050 pixels.
WTA is a part of WAP's WAE. WTA is an application framework for telephony services. WTA provides four services: WTAI, repository, event handling, and WTA service information.
WTAI defines a set of WTA-related functions in a wireless device that can be invoked via WML or WMLScript.
WTLS sits between WTP and WDP layers in the WAP stack, and is responsible for providing transport layer security between the WAP client and WAP Gateway or Proxy. WTLS is optimized for narrowband communication.
A Display Standard referring to a video adapter capable of a resolution of up to 1920 by 1200 pixels.
The WWW is a distributed Hypermedia System which is built on top of some of the services provided by the Internet. It is based on the Client/Server-Model, defining a Protocol for the exchange of information between WWW Clients and Servers.
X11 is a distributed window system that is based on the Client/Server-Model. In X11, the traditional roles of a Client and a Server are not distributed as usual, because the X11 Server is the local entity (providing the service of displaying data and accepting user input), while the X11 Client is the remotely running program, which uses the X11 Server to provide a GUI to the user. X11 is based on a Protocol, which makes it very easy to separate a (possibly heavyweight) program and its GUI. X11 is commonly used in Unix-derived Operating Systems.
X3D is the name under which the development of VRML is continued. X3D is based on XML and is backwards compatible with VRML. Furthermore, it is componentized, profiled, and extensible, which makes it possible to use X3D in very different scenarios, from high-end visualizations to lightweight applications.
X.500 is an open, distributed, online directory service which is intended to be global in scope. X.500 is a support service for data exchange which includes providing directory support for data communication services specified by other OSI application standards. The X.500 series of standards covers services available to users, the functional model and protocols connecting the component parts of the directory, an information framework and a schema of the information held by the directory, and a mechanism for allowing OSI components to authenticate each other.
X.509 describes two levels of authentication, simple authentication, based on use of a password to verify user identity, and strong authentication, using credentials created by cryptographic methods. The standard recommends that only strong authentication should be used as the basis of providing secure services. Public-Key Cryptography is used for strong authentication, but X.509 is not dependent on the use of a particular cryptographic algorithm, though two users wishing to authenticate must support the same algorithm.
Xanadu is an overall paradigm, an ideal and general model for all computer use, based on sideways connections among documents and files. This paradigm is especially concerned with electronic publishing, but also extends to all forms of storing, presenting and working with information. It is a unifying system of order for all information, non-hierarchical and side-linking, including electronic publishing, personal work, organization of files, corporate work and groupware. All data (for instance, paragraphs of a text document) may be connected sideways and out of sequence to other data (for instance, paragraphs of another text document). This requires new forms of storage, and invites new forms of presentation to show these connections. On a small scale, the paradigm means a model of word processing where comments, outlines and other notes may be stored conceptually adjacent to a document, linked to it sideways. On a large scale, the paradigm means a model of publishing where anyone may quote from and publish links to any already-published document, and any reader may follow these links to and from the document.
CMS is used to digitally sign or encrypt arbitrary messages. CMS describes an encapsulation syntax for data protection. It supports digital signatures and encryption. The syntax allows multiple encapsulation, so one encapsulation envelope can be nested inside another. Likewise, one party can digitally sign some previously encapsulated data. It also allows arbitrary attributes, such as signing time, to be authenticated along with the message content, and provides for other attributes such as counter-signatures to be associated with a signature.
XDuce is a typed Programming Language that is specifically designed for processing XML. One can read an XML document as an XDuce value, extract information from it or convert it to another format, and write out the result value as an XML document. Since XDuce is statically typed, XDuce programs never yield run-time type errors and the resulting XML documents always conform to specified types.
ASN.1 XER is a set of encoding rules that encode ASN.1 data in XML document syntax. While this encoding is not as compact as other encoding rules commonly used for ASN.1, it enables users to on the one hand use ASN.1's powerful syntax, and on the other hand generate data from it which can be processed using existing XML tools (such as XSLT). Furthermore, because XER uses XML syntax, it is human-readable, while all other ASN.1 encoding rules generate binary data.
A Display Standard referring to a video adapter capable of a resolution of up to 1024 by 768 pixels.
XHTML is a reformulation of HTML in XML. HTML is based on SGML and uses some features of SGML which are not available in XML (most notably, markup minimization), and consequently HTML documents typically are not valid XML documents. XHTML redefines HTML as an XML DTD, and also gives some recommendations how to use the markup in order to make XHTML compatible with older browsers, which only understand HTML (and thus may have problems processing XML syntax, for example the special form of empty elements).
XLink defines how to insert links in XML documents. It specifies a framework making it possible for XML applications to recognize XML elements as having link semantics. In addition to the simple, two-ended, unidirectional links which are well-known from HTML, XLink allows more general links, which must not be embedded in the document, can have any number of ends, and can be multidirectional.
XLL was the term under which the development of XLink and XPointer started, referring to both activities as a whole, but it is no longer used.
XML is a markup language for structuring arbitrary data. XML was designed to replace HTML, which was deemed too restricted with its fixed set of elements and attributes. Because HTML is based on SGML, but SGML itself was considered as being too complex for direct application on the WWW, XML was defined as a functional subset (a "profile") of SGML. XML defines data types (called "schemas") with DTDs, which originate from the document-centered view of SGML. However, XML is very successful in B2B scenarios, and as such is increasingly used for data exchange (as opposed to document exchange). Because data description requires other features than document description (eg, built-in data types and type derivation), XML Schema has been defined as a replacement for DTDs, which makes XML more usable for B2B scenarios.
XML Infoset is an abstract data set describing the information available from an XML document. For many applications, this way of looking at an XML document is more useful than having to analyze and interpret XML syntax. DOM describes an API through which the information in an XML Infoset (ie, the information available from a specific XML document) can be accessed from different programming languages.
XML Namespaces are used to qualify unique names in XML Namespaces documents which use schemas from different sources. This can occur because schemas (such as DTDs) are reused. However, if schemas are combined, it is possible that name conflicts appear. XML Namespaces defines a way how schema identification (through a URI) and names of a schema are combined to yield unique names.
XML Schema is an XML Schema Language for XML. After XML's success for B2B applications, it quickly became apparent that XML's built-in XML Schema Language, the DTD, did not meet the requirements of application developers. XML Schema has thus been standardized by the W3C and extends DTD considerably, in particular with a type system supporting type derivation, and with a number of built-in simple types (such as integer, float, date, and time). While XML Schema is much more powerful than DTDs, it is also much more complex, but it is very likely that over time XML Schema will replace DTDs.
XML-Data is a proposal authored by Microsoft for the definition of WWW Meta Data. The proposal has been used as input for W3C's work on RDF, which has the same application area as XML-Data.
XPointer enables addressing into the internal structures of XML documents. In particular, it provides for specific reference to elements, character strings, and other parts of XML documents, whether or not they bear an explicit ID attribute. XPointers can be used as fragment identifiers in URI references to specify a more precise sub-resource. Any URI fragment identifier that points into an XML resource must be an XPointer. XPointer is often used together with XLink, which specifies how to use hyperlinks with XML.
XML Schema is a rather complex XML Schema Language, partly because of its inherent complexity, and partly because of its XML syntax. In an effort to reduce the syntactic verboseness and complexity of XML Schema, XSCS defines a EBNF-based (and non-XML) syntax for XML Schema. XSCS is designed for human users, and transformations from and to XML Schema XML syntax are implemented using Java-based tools.
XSL is a Style Sheet Language that can be used for displaying XML documents. Using XSL is two-step process, the first step being a transformation of the XML document using XSLT, and the second step being the rendering of the result of the transformation, which is done using XSL-FO. While XSL covers the same application area than CSS, it is much more powerful, because the transformation step (using XSLT) can perform arbitrarily complex transformations of the XML document, while CSS is not able to make any structural changes to the XML document.
XSL-FO is an XML vocabulary for the formatting of documents. Being part of XSL, the normal way is to produce XSL-FO documents by transforming XML documents using XSLT. Even though the principles behind XSL and CSS (the other Style Sheet Language created by W3C) are quite different, it is planned to align the formatting model between XSL-FO and CSS, so that formatting engines can be based on the same code, both languages can be used to achieve the same results, and formatted results will look identical.
XSLT is a specialized Programming Language for transforming XML documents. Even though it is part of XSL and as such intended to be used for transforming XML documents into XSL-FO for presentation purposes, it is not limited to this application area. XSLT uses XML syntax (ie, it is a Programming Language in XML syntax), even though it is based on DSSSL (which uses a Lisp-like syntax). XSLT is particularly interesting in B2B scenarios, where XML documents must be transformed.
XSP is Cocoon's technology for building WWW applications based on dynamic XML content. An XSP page is a Cocoon XML document containing tag-based directives that specify how to generate dynamic content at request time. Upon Cocoon processing, these directives are replaced by generated content so that the resulting, augmented XML document can be subject to further processing (typically an XSLT transformation). XSP pages are transformed into Cocoon producers, typically as Java classes, though any scripting language for which a Java-based processor exists could also be used. Directives can be either XSP built-in processing tags or user-defined library tags. XSP built-in tags are used to embed procedural logic, substitute expressions and dynamically build XML nodes. User-defined library tags act as templates that dictate how program code is generated from information encoded in each dynamic tag.
Z39.50 is a standard for information retrieval, it specifies a Protocol for the behaviour of two systems communicating for the purposes of database searching and information retrieval. As a network application standard, Z39.50 is an open standard that enables communication between systems that run on different hardware and use different software. The Z39.50 standard was developed to overcome the problems associated with multiple database searching. Z39.50 simplifies the search process by making it possible for a searcher to use the familiar user interface of the local system to search both the local library catalogue as well as any remote database system that support the standard.