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

> Rick Jelliffe wrote:
> > The grammar-based schema languages are trying
> > to interpose some type system between markup structure
> > and the model, without any guarantee that their type systems
> > will be any easier to map to a model than the original structures
> > were. Witness XML Schemas, which is conceived in terms
> > of "components" (its model) but has no analog of "component"
> > in either its type system or its markup. TREX and RELAX
> > seem to snuffling for diamonds in the same sandpit, with as
> > much chance for success.
> 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).
> 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.

What sort of "semantic model" are we talking about? The ones I am familiar
with are concerned at the core with type hierarchies or at least things that
look awfully alot like type hierarchies.

Of course I think types can be represented in a very simple fashion i.e. any
constraint defines a type, and a type is no more nor less than a constraint.

> I don't believe the use of TREX and RELAX interposes a type system
> between an XML-based language and a semantic model, any more than the
> use of regular expressions interposes a type-system between a
> string-based language and a semantic model.

And I would say "nor any less than a regular expression interposes ..." that
is to say a regular expression defines a type. Thinking of types in this way
imposes no complexity on information models etc.  ... another way of saying
this is that the type system _defines_ the semantic model.