- More and more value switches from goods to information
- Information sharing needs well-defined structures
- Business agility and flexibility are critical success factors
- Standardized formats prevent lock-in and incompatibilities
- XML is the most successful format for structured data
- XML technologies are widely used and universally available
- XML for B2B enables better workflow engineering
- XML for B2C is a good interface between B2B and Web interfaces
- XML is a mission-critical success factor for optimizing ROI and minimizing interoperability risks in today's fast-moving globalized fragmented business landscape …
- XML Basics and how to apply them
- Describing classes of XML documents
- Combining different vocabularies of XML documents
- Selecting parts of an XML document
- Transforming XML into something else (or XML again)
- A more complicated way to describe classes of XML documents
- Even more ways of describing classes of XML documents
- How does all of this relate to databases?
- What to expect as future developments
- Assignments
- blogs as the common theme (the perfect XML application example)
- how to create an XML document representing a blog
- how to write a schema describing this document's structure
- how to select parts of the blog (posts, titles, comments, …)
- how to transform blogs (into HTML, RSS, Atom, …)
- how to extract blog information from an XML database
- Tools
- XML editor such as Altova XML Spy (XSLT and XQuery included)
- XSLT Processor such as Saxon
- XQuery Processor such as Saxon
- XML database such as MarkLogic or eXist
- Computer Science at Technical University of Berlin (TUB) (88-91)
- Ph.D. at ETH Zürich (92-97)
- Post-Doc at ICSI, Berkeley (97/98)
- Various activities back in Switzerland (98-06)
- teaching at ETH Zürich and FHNW
- working as independent consultant (training, courses, consulting)
- research in various XML-related areas
- Visiting Assistant Professor at the School of Information (since fall 2006)
- technical director of the Information and Service Design (ISD) program
- Course Web page:
http://dret.net/lectures/xml-fall07/ - Course mailing list: subscribe at
majordomo@ischool.berkeley.edu - no subject (leave blank)
- body of message:
subscribe i242 - Letter grade based on final exam (30' oral)
- Generated from XSLidy XML
- all Slidy presentations are generated from this source
242.xmlfor importing the syllabus into SylViAtoc.htmlfor displaying the summary on the course's Web page- Designed for online presentation and use (lots of links!)
- for printing, use
a
(all slides), and thens
(smaller font) a couple of times - A good real-world example for XML applications
- XSLidy is useful, but there is no interface (XML editing only)
- SylViA is useful, but there is no interface (XML editing or XSLidy export)
- My Online Glossary at
http://dret.net/glossary/ - suggestions, updates, corrections are very welcome (really!)
- XML-based and XSLT-generated HTML pages
- My bibliography at
http://dret.net/biblio/ - suggestions, updates, corrections are very welcome (really!)
- The World Wide Web Consortium (W3C)
- the organization which invented XML
- as well as (almost) all other technologies covered in this course
- XML is …
- … great for exchanging trees (if this is what you want to do)
- … platform-independent (even your mobile phone processes XML)
- … a foundation for other technologies (some of which we will look at)
- XML is not …
- … a programming language (ever programmed comma-separated values?)
- … capturing semantics (without higher-layer consensus, XML is worthless)
- … ensuring interoperability (we both use bits! we can interoperate!)
- Because you want to share data
- share it in a format which is widely used and easy to use
- enable others to use it on various platforms with existing tools
- Because you want to share data cheaply
- it is easier to use XML than to invent something new
- it is even easier to use an existing XML schema than to invent a new one
- Because you want to share data openly
- if you invent new formats, people must process them
- avoid applying the
security through obscurity
principle inadvertently - application-specific processing should be deferred to higher layers
- XML is often said to be
self-describing
- many people think this is the same as
self-explanatory
- the catch is what exactly it is you refer to by
describing
- Database data cannot live without a database
- database data is simply content, the structure is provided by a DBMS
- XML documents have their structure encoded within them
- compared to database data, XML in fact is
self-describing
- What is the gap between
self-describing
andself-explanatory
? - it is impossible to find out how the document could be modified
- there are no semantics associated with neither structure nor content
- so
self-describing
means, you can guess a lot, but you maybe wrong
- XML is not a binary format, it is based on Unicode
binary structures
cannot (or rather should not) be described using XML- Multimedia formats often are binary
- image formats such as GIF, JPEG, and PNG
- audio formats such as MP3 and AAC
- video formats such as MPEG4 and H.264
- But: multimedia also uses many XML formats
- vector graphics formats such as Scalable Vector Graphics (SVG)
- Synchronized Multimedia Integration Language (SMIL) for describing presentations
- Not all data is easily represented by trees
- overlapping markup (multiple
views
of the same content) - graph-like structures which are less constrained than trees
- What is it that you have in your tree?
- XML encodes a structure purely on the syntactic level
- what the structures mean is in no way described by XML
- XML structures must be accompanied by semantic descriptions
- XML can be used in different ways
- people should be able to use your XML directly using standard tools
- if they absolutely need a set of special tools, something is wrong
- XML is hip, so everybody wants to use it
- many things have been created ad-hoc and without much planning
- if you start something which is XML-based, use XML responsibly
- if you have to use some
bad XML
, complain about it - Finding the balance can be hard
- XML is great for prototyping and experiments
- once you decide to redesign your XML, it may be too late
- XML documents may be short-lived, XML schemas are definitely not
- Early Web: URI+HTTP+HTML
- URIs identify resources (in a human-readable way)
- HTTP retrieves resources (using a simple protocol)
- HTML is the resource format (using a simple data format)
- The early Web was a distributed hypermedia system
- not designed by hypermedia researchers or companies
- simple enough to be adopted very fast
- The Web today uses many different technologies
- URI+HTTP+HTML for basic Web publishing
- CSS & JavaScript (maybe even Ajax) for advanced publishing
- JavaScript & XML (a.k.a. Ajax)
- scripts dynamically loading data from a server
- machine-to-machine interaction: the server and the script
- The Web was designed for humans
- HTML is a language for describing page layout and links
- machines were only used for implementing it
- Search engines were the first machine users on the Web
- they made the Web's success possible
- they demonstrated how hard it is to
understand
HTML pages - search engines are still a very active field of research
- A bigger Web needs more automation
- HTML is a format for
dead ends
- HTML is good for rendering Web pages
- HTML is bad for understanding Web pages
- the browser is a
dead end
(from a machine's point of view) - Web growth in the late 90's was enormous
- everybody was putting information
online
- but this information was inaccessible for machines
- How can this information be made accessible to machines?
- HTML is not the right format (slightly better than fax machines)
- there was no other widely accepted format for structured data
- Information should be published in a machine-understandable format
- HTML is good for rendering Web pages
- HTML is bad for understanding Web pages
understanding
is the key term here: application semantics!- Information should be published in application-specific formats
- HTML is one application: Rendering documents for humans
- machines need other structures to process Web content
- 1996: W3C Working Group
SGML on the Web
- HTML is just one document type defined with SGML
- SGML is a very complex and expensive technology
- how can SGML be made easily and widely usable?
- Standard Generalized Markup Language (SGML)
- a language for designing document types
- a very complex standard with many expensive and non-interoperable implementations
- Hypertext Markup Language (HTML)
- implements a simple SGML document type
- its syntax is SGML syntax, it is not defined by HTML itself
- uses very few SGML features, dedicated processors are rather easy to build
- Extensible Markup Language (XML)
- a language for designing document types (i.e., classes of documents)
- a greatly simplified version of SGML, omitting many obscure features
- a specification with no optional parts!
- XML's idea was that content should be published as XML
- stylesheets could then be used to render human-readable views
- machines could simply use the underlying XML
- There are (almost) no XML documents on the Web
- stylesheet support depends on browsers (software has a long life!)
- many content providers do not want to publish machine-readable data
- There are many XML documents behind HTML documents
- content does not have to be made public in a machine-readable way
- browser-independent HTML can be produced from XML
- XML technologies can be leveraged on the server-side
- XML is not used as intended, but it is very successful
- as a server-side foundation for Web publishing
- as a B2B-focused format with no Web publishing in mind
- XML has been successful because of different reasons
- being there at the right time (Internet bubble)
- politically correct (the W3C is OS-agnostic)
- technically sound (simple and no optional parts)
- human-readable based on a well-known syntax
- great for rapid prototyping and experiments
- Very small: Messages from sensors
- e.g., building automation or car electronics
- mostly implemented in hardware or firmware
- Very large: Genome sequences
- encoding the results of genome analyses
- yields very large XML documents (several gigabytes)
- Very different processing requirements
- very fast processing (time critical applications)
- memory-conserving processing (very large documents)
- incremental processing (streaming)
- random access (only small parts required)
XML is the ASCII for the 21st century
- information professionals should know and use XML
- you will see it in many projects
- you will hopefully use it in many projects
- you will be able to build and test prototypes very rapidly
- What do you need for using XML?
- XML and some kind of schema language
- XSLT for processing it
- XML is a syntax for trees
- trees are just structured data
- for doing something useful, you must understand the trees
- Schema-based sharing of concepts is possible
- HTML works great because everybody is using it
- Anything beyond HTML's capabilities needs a new schema
- General sharing of concepts is hard
- the AI community tried for decades and failed
- micro-formats are a more humble approach to
reusable shared concepts
- agreement in communities gets exponentially harder with their size
- Technologies for describing concepts
- the foundation of successful interaction is mutual understanding
- describe your XML using Semantic Web technologies
- XML core technologies do not convey any meaning
- XML is a language for exchanging trees
- XML schema languages describe what trees may be exchanged
- XML schema languages are for markup design
- Semantic Web technologies have received a lot of attention
- and a lot of research funding
- success for the most general approaches is questionable
- proven failure as demonstrated by AI's failure
- modest approaches are much more promising and likely to succeed
, but the important point is that they are on the same level as the text nodes of the mixed content.
