Strong Typing in SGML and XML

Peter Murray-Rust Peter at
Wed May 7 22:41:48 BST 1997

In message <libSDtMail.9705071132.28775.altheim at mehitabel> altheim writes:
> Peter at (Peter Murray-Rust) writes:
> > In message <199705071326.JAA12115 at nathaniel.ebt> gtn at (Gavin Nicol) writes:
> > > 
> > > RE processors are easy to implement, and there are a great number of
> > > them available for free. There are a number of specifications that
> > > could be used: I would recommend something like the POSIX ones,
> > > suitably extended.
> > 
> > Good.  Where is a volunteer to crack up a Java one?
> Well, after reading Jeffrey Friedl's book "Mastering Regular Expressions"
> (O'Reilly), I would heavily caution everyone to make sure we advocate and
> develop to a *single* RE specification, as it seems very evident that there

I thought this was taken for granted - that there would be a single RE in
all XML-l[ai]n[gk] specifications.  I also assumed (naively?) that POSIX
defined such an RE, and we merely needed an implementation.  There might well
be subsidiary questions such as 'do we want to implement a subset', 'are there
any clashes between RE syntax and XML syntax', 'are PEs expanded before
evaluating the RE :-)', etc.

> is such a variance between the RE processors in perl, Tcl, sed, awk, vi, etc.
> that having RE inconsistencies among XML applications would be worse than
> having no RE support at all.

Fully agreed.

> If we choose a code base that contains more RE features than the minimal
> set supported by all RE processors, we need to be clear which features
> are part of and required by XML. (This sounds like a mess to me.)

Since XML-LINK-TEI has shrunk since its first airing, I suspect that there
is a desire not to overreach.  Certainly we should not force implementors
to have to work hard to comply to unnecessary features.  (For all I know 
some REs would be sufficiently powerful to act as XML parsers :-)


Peter Murray-Rust, domestic net connection
Virtual School of Molecular Sciences

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