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Re: Type and Structure Re: ASN.1 and XML

Rick Jelliffe wrote:

> From: "James Clark" <jjc@jclark.com>
> > I do not see either TREX or RELAX as trying to interpose a type
> > system between markup structure and the model (I assume you
> > mean a conceptual/semantic model).
> Nevertheless they do.
> > In fact, this is one of the big differences in philosophy I see
> > between TREX and RELAX on the one hand, and W3C XML
> > Schema on the other.
> Yes, I think that is a very important point.  Schematron can be added to
> list also with TREX and RELAX, in that it also comes from the view that
> adding type information to the infoset to be used for general processing
> adds a level of complexity (i.e. it requires schema processing rather than
> simple keying from the element's generic identifiers) that is utterly the
> wrong design for the web.

I am not sure this is entirely fair. As I see it, the problem isn't types
per se, rather how it is done. So when you say that the type system is
_interposed_ between the document and the conceptual model, this is bad, but
the type system need not be interposed.

I think we should make the distinction between a *bad* type system and

For example, if a program knows that an input XML document is valid, it
*can* make assumptions regarding the information keyed by element generic
identifiers -- of course this is the XML 1.0 notion of types. Similarly a
valid document has a type.

> ... the rest of the XML community seems on a
> pro-grammar crusade that perpetuates the disconnect between concept and
> expression.  One thinks about things in some terms, then tries to fit
> thoughts in a grammar.

_types_ are not the problem here, because one can have conceptual and
semantic types, types need not be syntactic. furthermore one _can_ and
perhaps we should encourage the practice of designing XML document
structures in ways that naturally reveal the conceptual model of how the
document _is intended_ to be used. not that this will always be possible,
but to me, that is the essence of well-formedness: I should be able to read
the document (perhaps with elements indented etc), and come to some
understanding of what the document is intended to represent, what
information it is intended to convey.

> In doing so, we are modeling the concepts, but in a way that is entirely
> amenable to conversion to validators (either to a grammar system or
> something like Schematron).  Some conceptual structures have markup
> representations; some do not--but the thing that determines them is not
> mechanics of constructing a grammar: they correspond to logical structures
> that are not (and sometimes cannot be) marked up as the element tree.
> Grammars should be an implementation technique, not the nub of the

Fair enough. I just consider part of being readable is being understandable,
and we should strive to make our formats understandable. There _is_
something to be said for good grammar

> I hope that makes it clearer the scope and nature to why I would lump
> and TREX in with XML Schemas in regard to types.

Well, I lump RELAX,TREX,DTDs,XML Schema, RDF Schema, DAML and Schematron
together with Examplotron in regard to types. so there ...