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Don, <snip> > Also standard DTDs can not adapt to change. What do you do when the > standard DTD for electronic devices must be changed to include performance > data (i.e. WinMark for Intel machines)? The problems are simply > mindboggling (well, my mind is easy to boggle). One approach that really appeals to me is based on a two-pronged effort to create standard tags *and* standard DTDs, and relies on the fact that there is really a working mechanism for extending DTDs through inheritance (which I guess is still not entirely the case). Standard tags would be a bit of a hack, but probably very useful in a pragmatic sense. For example, you might be able to say certain things about a TITLE tag, or a PRICE tag, or whatever, just on the basis of the name, regardless of the actual DTD being used. If these conventions were well-known, this could be of great use when defining a new DTD (i.e. "Let's call the tag PARAGRAPH and not PARA because this is what will be recognized by search engines"). Inheritance is *not* a hack and really seems like the way to go for more ambitious implementations. To take your example, the DTD for electronic devices might contain tags for VENDOR, PRODUCTNAME, PRICE, CATEGORY, etc. If I want to find all CD player devices from Sony that cost less than $99 then I can query based on this standard DTD. Vendors who want to include more information just derive a new DTD with all the standard tags, as well as vendor-specific ones (for benchmark figures, for example). The non-standard tags may not be available for querying, but the information in the standardized base DTD would be. This becomes even more powerful with multiple inheritance. I can whip up a DTD for my new portable XML viewer/expresso brewer, imported from Kazakhstan, just by grapping the standard DTDs for hand-held electronic devices (derived from general electronic devices but adding tags for SIZE, WEIGHT and BATTERYLIFE), for food processing equipment (also derived from electronic devices but a tag for FOODTYPE) and for imported goods (with tags for COUNTRYOFORIGIN, EXPORTTARIF, etc.). This would let users find my product by querying for all portable devices weighing under 200 grams which can process coffee and which are produced in Central Asia. I really believe the world needs XML to get a grip on information explosion. The approach suggested by the original poster is great, and with plug-and-play DTDs I don't see any real technical reason why it shouldn't work. As an initial implementation, the approach based on GI only would no doubt be a good workaround. Matthew xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...)
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