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   Re: Proposal for src files

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  • From: matthew@praxis.cz (Matthew Gertner)
  • To: <xml-dev@ic.ac.uk>
  • Date: Thu, 2 Apr 1998 19:29:17 +0200


You make a lot of valid points, but I can't held feeling that your stance is
a bit radical. The fact of the matter is, I asked myself the other day
exactly how HyTime handles inheritance and spent at least an hour trying to
find the answer. Of course, I wasn't entirely sure that I understood at the
time and I certainly couldn't explain it to you now without looking it up
again. And this despite a pretty solid grip on SGML and OO technologies, as
well as a thick stack of SGML-related bookmarks in my browser.

HyTime is an amazing piece of work, but it is never going to attain critical
mass in its current form. As you say in your message, this is just fine: it
is a big tool for big problems and requires specialist intervention. On the
other hand, seen it this light it clearly isn't a general answer to the
problem of mixing and matching XML DTDs.

XLL is a great example of the right approach to take in regard to using DTDs
as extensible schemata. First of all, it reduces the intimidation factor
inherent in the 500 odd pages of dense text that make up the HyTime
standard, by extracting only the relevant bits. Moreover, it cuts out some
of the complexity that makes HyTime somewhat unapproachable for many people.
Nevertheless, it steals many of the good ideas first advanced by HyTime (and
TEI linking); I don't think that anyone is suggesting that this work go to

I really like Peter's idea of trying to use the resources of XML-DEV to
produce a concrete proposal for extensible XML DTDs. Let's start throwing
out some ideas and see where this gets us! Having a HyTime expert (and I see
several) onboard would obviously be invaluable.

Many, many years have gone into research and practical work on
object-oriented design, much of which was focused directly on the problems
inherent in producing extensible schemata. My feeling is that this work
could be mapped almost directly onto XML. There was a question recently on
the list about sticking an arbitrary element type into the content model of
an element type in an existing DTD. The fact of the matter is, this simply
doesn't work. On the other hand, DTDs can be designed for extensibility, and
derived DTDs can then include digital signatures and the like by extending
the content model. This seems to be the idea behind XML-Schema, which would
be an excellent starting point for this kind of effort, IMHO. More later...

>Ah. My point is that, if that's all it is, why bother? If you can parse
>DTDs sufficiently to generate XML versions, why bother generating the XML
>version? You've already parsed the thing the data's already yours to
>manipulate.  If you do want the XML version, then go back into the c.t.s
>archives and find Wayne Wohler's posting (I'm sure he posted something
>about it). In any case, it's a pretty obvious design effort and the result
>should be uncontroversial except for some arbitrary design choices (use
>attributes? etc.).

Because there are significant advantages to having a single syntax for both
data and metadata. What about the standard DTD syntax makes it _the_ syntax
for schema exchange for now and all eternity? I'd love to pull my schema
definition into my XML browser, print it with an XSL stylesheet, etc., etc.
A standard XML-based schema language would let me do this without having to
go through the effort of maintaining an alternate syntax and conversion
tools. What I am sensing is that, if there is going to be a standard syntax
for schema exchange, people are not convinced that the existing syntax is
the right one. I'm a bit confused by your argument, to the extent that you
say, on the one hand that the effort is trivial, and on the other that it
should not be underestimated. I haven't seen the work by Wayne Wohler, but
if I may ask a naive question: isn't this what XML-Schema is all about?



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