Re: a or b or both - mystery..

[Murali Mani <mani@CS.UCLA.EDU>]

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
> ftp://ftp.informatik.uni-freiburg.de/documents/papers/brueggem/habil.ps?
> 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
http://www.cs.ucla.edu/~mani/xml/papers/conferences/WebDB2001/td-main2.ps