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- From: "Matthew Gertner" <firstname.lastname@example.org>
- To: <email@example.com>
- Date: Fri, 20 Feb 1998 14:11:42 +0100
> 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.
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