Don't you mean "In my mind's eye they don't share a content model"?
You are making statements about the characteristics of systems you
haven't seen yet (OO Schemas or whatever) and certainly haven't used.
Once you _can_ declare them subclasses of a parent grouping element,
you might find you start doing things differently. You might not, but
you can't really make such statements until we've got some proposals
on the table.
> Tables and figures are also related as "block-level objects" (in many
> DTDs), but also do not share a content model or attributes. This is why I
> feel strongly that element type subclassing is quite different from
> inheritance in documents, just as in OO.
>
I know your opinion here. But inheritance is just a subset of
subclass relationships (subclass is an as-a relationship, inheritance
is an is-a relationship, and all is-a relationship are also as-a
relationships). We have yet to see how this plays out in XML, and
even though you AF gurus may have a head start, I don't think even you
have enough info to make categorical statements. But it'll be an
interesting conversation.
> > Are you calling for the resurrection of SHORTREFS? Content models should
> > ideally address the abstract syntax tree. Lexical constraints address
> > content. If you want to cross them, you need something like SHORTREFS (or
> > BNF.
>
> Sorry, I was speaking loosely. I'm more interested in constraints at the
> tree level than lexical constraints. But I don't see why you think that
> lexical constraints need something like SHORTREFS or BNF. What about
> regular expressions? What would be fundamentally wrong with something
> like this:
>
> <!ELEMENT FOO (LHS,"=",RHS)>
>
Datatag?
What's wrong is it doesn't identify the "=" as an operator, so either
you know it's an = sign by default, in which case it's redundant,
or you have an expression but no way to know what the operator is.
You are mixing levels - you've got parsing and lexing mixed, which is
what made SGML so twisted.
Matthew
matt@veosystems.com