Another look at namespaces

[Rick Jelliffe]

From: James Tauber <jtauber at jtauber.com>

>> This distinction, that the Document Type Definition is not the same
as the
>> markup declarations, is as old as SGML.
>
>SGML makes the distinction and I think it is a good one but I don't
think
>XML does. In XML a DTD is the (formal)grammar defined by the markup
>declarations and no more.

Sure, in XML "This grammar  is known as a document type definition, or
DTD."
But that just means that in XML we have to use some other term instead
of
"document type", for example "language".  It does not alter my point.


>Whether one views:
>
>    vocabulary = names + semantics
>or
>    vocabulary = names + syntax + semantics
>
>possible determines their standing on the number of namespaces XHTML
1.0
>should have.

I think
   namespace = names
    vocabularies = names in namespaces + semantics possibly
        (I can have a vocabulary composed of names from different
namespaces)
   syntactic schema = names in namespaces + syntax
        (e.g. XML DTD)
    language = names + syntax  + semantics
        (where the syntax ideally uses some grammar that actually
captures the
        amount of cohesion between elements.)

Actually, there should be a difference distinguished between a model and
a schema. The schema captures/describes everything about a syntax; the
model merely  captures/describes everything convenient.  So the
statecharts
in UML allow guard conditions, to allow extensibility: constraints which
don't fit into the grammar types allowed by UML statecharts can be
notated still.

Rick Jelliffe



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