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RE: multiple types

> > The operative word is *conforms*... type is painted on
> > data by a set of assertions.
> I think this is a really important point. Example of this are "Document
> Types" aka DOCTYPE which defines a document type as validity
> w.r.t a DTD (a set of constraints). Another example is XML Schema regular
> expressions which define a type as a pattern conformed to. Another
> example is what Murata Makoto recently posted about "Hedge
> Regular Expressions" which related to TREX, RELAX and perhaps
> what Examplotron is growing into. Yet another example is
> Schematron which directly defines conformance in terms of
> assertions. So yes.

Just to follow up with one last though before I disappear for a
couple of days.

I think people are getting confused between instances and type
definitions. In the context of a type definition, it makes great
sense to use "is-a" and "has-a" and "extends", etc. This is
again, defining the *type*, not an instance.

When a chunk of data comes along, one then asks "does it conform
to the definition of this type?" (does it have a...?).

These are very different things from actually generating the