Re: Tim Bray on "Which Technologies Matter?"
Marcus Carr wrote: > >... > > We accept that HTML and XML are designed for different purposes from each > other, so why is there so much resistance to accepting SGML as a third facet? I can define the difference between HTML and XML in one relatively easy to understand sentence: "XML allows you to invent your own element type names which allows it to more descriptively represent a much wider range of data than HTML, with its fixed list of element types. Therefore XML is more appropriate when the HTML element type set is not sufficient. HTML has a predefined set of hypertext-oriented element types supported by many software products such as web browsers. Therefore HTML is more appropriate than generic XML when you are trying to achieve a high level of interoperability in hypertext publishing." Now what would we say to differentiate XML from SGML? How would I decide when my customers should use SGML instead of XML? What sort of problems are uniquely suited to non-XML SGML? SGML's survival as a technology separate from XML will depend on the ability of its proponents to articulate its appropriate problem domain and to ground this articulation in technical features that XML lacks. > Another turnaround - if XML matters and SGML doesn't, why haven't we seen the > demise of SGML? The functional difference between SGML and XML is sufficiently minor that it is seldom worth the effort to switch one way or another. Furthermore, insofar as XML is officially a subset of SGML, SGML must (in theory) live at least as long as XML. But is anyone using SGML features that were left out of XML? CONCUR, LINK, DATATAG, OMITTAG, RANK, SHORTTAG? I still use some for my personal projects but I don't encourage my customers to. If the only difference between SGML and XML in common usage is the empty-tag and processing instruction syntax then SGML survives but not in a sense that I find very meaningful. Did SGML matter? Yes, of course, without it XML would not exist or might well be radically different (s-expressions?). Is SGML a thriving, growing technology separate from its XML incarnation? I personally do not think so. SGML has achieved its success under the name XML. Paul Prescod
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