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AI researchers I've talked to laugh out loud. So much of the web hype ignores lessons learned. It isn't that the Semantic Web, XML et al don't work: it is that what is promised and touted usually is beyond the technology and infrastructure of a WWW-like system. Will it work? Eventually if the slow pace doesn't kill it with boredom. Lessons from Popsicle sticks: Why did the boy stick a hose in his friend's ear? He wanted to brainwash him. Self-describing and extensible are two of the bigger XML hypehose words. The VRML to X3D project has been amazingly revealing. From the first to now almost the last, one message has had to be posted to the developers list: XML is just syntax. It is stupefying how many VRMLers didn't get the implications of that and not because they aren't bright well-trained CS majors but because VRML97 was clever. The syntax was lean and mean, the curly brackets looked enough like the coding style they were familiar with, the structure reflected a node system that was enough like the OOPies they implemented that the whole thing made elegant sense. The trick was, VRML isn't a metalanguage. It has exactly one application. The abstractions of the node types don't appear in the syntax, just in the specification. So the metalayer confusion has been horrific. That is working out now, but it took a lot longer than anyone would have guessed. Other than interoperable tools, so far, XMLizing VRML hasn't improved it much. We already could take XSLT and output VRML97, so the metadescription to rendering declaration pipeline worked. Using an XML editor to create VRML without the ability to pick on graphics objects improves nothing. Over time, namespaces and XSLT templates do result in a library of well-tested, well-understood artifacts that really can improve the lot of the VRML author, but for the VRML rendering implementor, it's a slow slog through the trenches of a verbose syntax with structural rules quite different from the lean world of VRML (VRML has no root). What we may get eventually are standard tools for profiling but so far, namespaces don't play a critical role in X3D. A metalanguage with syntax unification as its primary legacy exacts a price from the implementors. SGMLers know this one. You don't get much from the metalanguage itself; all the power comes from the application language frameworks devised for it. The so called complexity of XML comes not from XML but from the XML systems, the interoperating applications. This is dull news but it is what makes the press yammer for standard DTDs and schemas, makes the XML-Devers want to refactor the languages and folks, that is business as normal. len -----Original Message----- From: dehora [mailto:dehora@e...] > From: Rick Jelliffe > But I do agree that the term "self-describing" does seem open > for misinterpretation by anyone who has not looked at XML for more > than a minute: it may suggest that XML forces one to use names > from some global controlled vocabulary, or that it does more than > a simple sanity check on the names. In the XML world, 'self describing' seems to mean, self-describing, ie, XML data holds all the information needed to process and understand it. The problem is not with human readers (heck, they'll interpret almost anything), but that calling XML self-describing ascribes magical properties to, and/or magically simplifies machine understanding of, the data (presumably due to the data being tagged). Which is likely as not to mislead and eventual disappoint many people. Certainly I'd like to know what descriptive power XML has that would allows us to declare victory in this regard and throw away all our domain specific procedural code and business logic, replacing it with a general problem solver. AI researchers must be kicking themselves ;).
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