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Re: a or b or both - mystery..
- From: Murali Mani <mani@CS.UCLA.EDU>
- To: Marcus Carr <email@example.com>
- Date: Mon, 16 Apr 2001 19:50:48 -0700 (PDT)
let me get back to the examples later. I think her paper should give.
On Tue, 17 Apr 2001, Marcus Carr wrote:
> I didn't get that impression from her conclusions - are you referring
> to the paper located at the other end of
> On the contrary, it appears that she contributed her "decision
> algorithm for unambiguous expressions" to James Clark for his SGML
> parser. Ambiguity in SGML was occasionally inconvenient, but never
> more than that. My understanding was that the requirement for
> deterministic models was a concession made to those who were writing
> parsers at the expense of those who were creating DTDs. It was no big
> deal though - you learned to spot where problems might occur and
> avoided them.
No - this information is based on personal contact with her indirectly
over the last few months (I work with someone who has collaborated with
her a *lot*)
> > I also heard this: XML Schema WG has discussed deterministic content
> > models a lot, and they decided to use deterministic content models largely
> > for parser simplicity -- which I think is a non-valid reason at this
> > point.
> I suppose the working group felt that if this aspect of a processor
> was going to be made more complicated in XML than it was in SGML, it
> would discourage the writing of processors. Given that there were
> (arguably) only ever two nearly complete SGML (James Clark's and
> OmniMark) parsers, I tend to agree with them.
I think you know that TREX is from James Clark, and I think James Clark
strongly believes in non-deterministic content models for ease of use.
cheers - murali.
PS: The issues are not just expressiveness when you get to document
processing, but closure properties are *very* important, and it gets
really messy as XML Schema is *not* closed under 99% of the operations
that anyone will need.
I am not sure whether I should give this, but I think this is a decently
prepared report, written largely by my friend, but it is my work also, I
think some people might find it useful -- it is available at