XML: Whines and Battles - More on DTD's
More on DTD's...
Writing a full-blown, industrial-strength DTD is a non-trivial task. Many people are working on producing XML versions of popular DTDs like HTML (for compatibility and ease of transition), DocBook (computer documentation), TEI (literary, historical, and scholarly documents), CALS (military documentation, but including a widely-used table definition), ISO 12083 (article and book publishing), and many others.
But if everyone can write their own DTD, or use an existing one, how does the browser know how to display the pages that use it? This is where stylesheets come into their own. Theyre not a new idea the concept has been around for nearly 30 years, although theyve been called by other names, eg macros but what is new with XML is that although the stylesheet language is a separate development, its being done alongside the markup language, rather than several years afterwards.
The typographic display of HTML was left to the browsers, and the use of stylesheets is only now becoming common, many years after their original proposal. However, the final proposals for the XML companion stylesheet specification, XSL, probably wont be ready before the end of summer 1998. And although both big browsers have committed in one way or another to XML, to the extent of pulling out their parsers and waving them at each other, a fully-fledged XML browser is not quite ready yet, either.
However, software is coming to the rescue here too: ArborText has brought out an XSL stylesheet editor, which is ingenious, but still requires a bit too much foreknowledge of the theory behind XSL and DSSSL (ISO 10179, the formal stylesheet and transformation language for SGML). There are a number of similar other products in development, but its going to be up to the editor makers to provide a styling system as easy to use as the ones you find on full SGML systems like Inso Corps DynaText and Synex browsers.
While developers can plow ahead, content authors have to either wait and see what software becomes available later this year, or get stuck using the early editors and be prepared to change. The old question for content creators of "which system to use?" can be answered with the philosophy of established Internet practice: be liberal in what you accept; conservative in what you produce. With so much software available and in development, it should become easier to adopt a more flexible approach: author in whatever editor is most comfortable for you; serve whatever markup encoding your readers want (HTML, XML, full SGML. . .); and archive in whatever you deem to be the most useful long-lasting format. By which time itll be question time again.
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Peter Flynn has over 25 years of experience in computing, communications, systems and data analysis, data processing information management, training, and consultancy. The author of The World-Wide Web Handbook and the XML FAQ, Flynn is involved in many research and advisory activities including the IETF's former Working Group on HTML, and he is currently a member of the W3C's XML SIG as well as several software user groups. He is a Project Manager in the Computer Centre at University College Cork, Ireland, and is a consultant with several research projects in the EU and the USA. as well as with the text management consultancy Silmaril. His book _Understanding SGML and XML Tools_ is being published by Kluwer in July.
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Created: May 11, 1998
Revised: May 14, 1998