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Future Markup

Future Markup. Steven Pemberton CWI, Amsterdam Chair, W3C HTML Working Group. HTML as an SGML Application. SGML: an international standard in 1986 It is a Meta-language that describes data formats, using DTD’s (Document Type Definitions)

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Future Markup

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  1. Future Markup Steven Pemberton CWI, Amsterdam Chair, W3C HTML Working Group

  2. HTML as an SGML Application • SGML: an international standard in 1986 • It is a Meta-language that describes data formats, using DTD’s (Document Type Definitions) • Describes structure, not presentation<H1>HTML as SGML Application</H1> • Used for HTML in early 1990’s

  3. HTML • Netscape and Microsoft start adding to HTML: mostly presentation-oriented tags (like <BLINK>) • The World Wide Web Consortium (W3C) started effort to: • Keep HTML Pure • Do presentation via Cascading Style Sheets (CSS)

  4. CSS • CSS is a separate language from HTML that allows you to specify how an HTML document, or set of documents, should look • Separates content from presentation • HTML is a structure language again

  5. Advantages of CSS • Makes HTML easier to write (and read) • You can define a house style • Compatible: you can still see the content on non-CSS browsers • Pages are much smaller • Accessible to sight-impaired • ...

  6. By the way... • Check your logs: more than 90% of people browsing now use a CSS-enabled browser • You never need to use the <FONT> and <FONTFACE> elements again!

  7. Documents • HTML was designed for just one sort of document (scientific reports), but is now being used for all sorts of different documents • You could use SGML to define other sorts of document, but SGML is notoriously hard to fully implement

  8. Enter XML • XML is a W3C effort to simplify SGML • It is a meta-language, a subset of SGML • One of the aims is to allow everyone to invent their own tags • DTD is optional: a DTD can be inferred from a document

  9. Consequences • The requirement of being able to infer a DTD from a document has an effect on the languages you can define: • Closing tags are now required<LI>....</LI> <P>....</P> • Empty tags are marked specially <IMG SRC=”pic.gif”/> <BR/> <HR/> (or <HR></HR> etc)

  10. Consequences 2 • CDATA sections must be marked as such (if they contain “<”, “&” etc.): <SCRIPT> <![CDATA[ ... script content ... ]]> </SCRIPT>

  11. Not Like This <H1>XML</H1> An underlying problem with HTML is that ... <P> You could use SGML to define ... But Like This <H1>XML</H1> <P> An underlying problem with HTML is that … </P> <P> You could use SGML to define ...</P> By the way: <P> is not like <BR>

  12. Consequence of XML • Anyone can now design a (Web-delivered) language • CSS makes it viewable <address> <name>Steven Pemberton</name> <company>CWI</company> <street>Kruislaan 413</street> <postcode>1098 SJ</postcode> <city>Amsterdam</city> <speaker/> </address>

  13. So do we still need HTML? • XML is still a meta-language • There is still a perceived need for a base-line mark-up • HTML has some useful semantics, both implied and explicit (search engines gladly use it, for instance)

  14. HTML as XML application • Clean up (get rid of historical flotsam) • Modularise – split into separate parts • Allows other XML applications to use parts • Allows special purpose devices to use subset • Add any required new functionality (forms, better event handling, Ruby)

  15. Differences HTML:XHTML • Because of the difference between SGML and XML, there are some necessary differences, for instance: • Use lower case: <p> not <P> • Attributes are always quoted: <th colspan=”2”> • Anchors use id attribute not name (and not just on <a> by the way):<a id=”index”> <p id=”top”>

  16. Example <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head><title>Virtual Library</title></head> <body> <p>Moved to <a href="http://vlib.org/">vlib.org</a>. </p> </body> </html>

  17. Namespaces <html xmlns="http://www.w3.org/1999/xhtml"> <head><title>A Math Example</title></head> <body> <p>The following is MathML markup:</p> <math xmlns="http://www.w3.org/TR/REC-MathML"> <apply><log/><logbase><cn> 3 </cn> </logbase> <ci> x </ci> </apply> </math> </body> </html>

  18. Semantics Differences • Presentation  use CSS • Links  use Xlink or Schemas • Forms  use CSS? • Images etc.  use Xlink • (Natural) language of elements  use xml:lang attribute

  19. Transition • XHTML 1.0 has been carefully designed to make use of ‘quirks’ in existing HTML browsers • Use of a small number of guidelines allows XHTML to be served to HTML browsers

  20. Examples of Guidelines • Use space before / of empty elements: <br /> <hr /> <img src=”foo.gif” /> • Use name= and id= on <a>: <a name= ”index” id= ”index”> … </a>

  21. Conclusions • XML with related technologies gives you the freedom to define and deliver your own document types • HTML is still needed as a base-line markup • The new HTML gives a transition path to the future

  22. The State of Things • New generation of XML+CSS browsers emerging • Many XML applications appearing • Major companies planning XML as output(Adobe PDF, MS Office 2000) • Now: HTML4 as XML, Conversion software • This year: Modules, Subsets, Extensions, Profiles, New Forms

  23. To Find Out More • All XHTML developments are made public at www.w3.org/Markup • Members of W3C can also look at www.w3.org/Markup/Group

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