What is a namespace ... really?

[Borden, Jonathan]

David,

	My mind is still out on this topic. I've had a look at Microsoft's XML
Schema stuff in IE5 b2 however, and currently when the namespace uri starts
with "urn:" the namespace behaves as you desire. When the namespace uri
begins with another prefix, the implication is that this points to a schema
definition.

	I don't see a problem with this one-to-one relationship, after all, a
namespace *is* defined by a uri, so... and I don't immediately see why this
precludes inclusion of elemements from different namespaces.

	I think the idea is that if a namespace is defined by a uri, it may inherit
a meaning associated with that uri, for example, suppose the uri was a .DTD,
would this cause a problem or work any less well than a DTD which defines a
default namespace and is specified in a <!DOCTYPE definition?

Jonathan Borden

>
>
> Borden, Jonathan writes:
>
>  > This is the *current* state of affairs. There are people who also
>  > believe that in the future the namespace concept is to be extended
>  > to incorporate Schema definition. That is, when a namespace URN
>  > points to a Schema definition, the Schema may, can or will be
>  > enforced in the same way that a DTD is enforced by a validating
>  > parser and a <!DOCTYPE definition.
>
> Ack! No!  Please don't hardcode a one-to-one relationship between
> schemas and namespaces.
>
> A single schema could define structures using elements and attributes
> from more than one namespace, and elements and attributes from a
> single namespace can be used and structured in many different ways.
>
> SGML people handle this problem in a fairly clumsy way by using public
> identifiers for indirection and then swapping entity catalogues at
> different stages of production.  We can do better if do what a
> database designer does for many-to-many relationships: add separate
> associations between the namespace and the schema.
>
> The alternative would be to rely on HTTP content negotiation to get
> the kind of schema you want, and that is a pretty grim prospect
> (especially for people with web sites hosted by large ISPs who really
> aren't going to let them fiddle with the web server).
>
>
> All the best,
>
>
> David
>
> --
> David Megginson                 david at megginson.com
>            http://www.megginson.com/
>
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