Re: Namespaces, schemas, Simon's filters.

[Ronald Bourret <rpbourret@rpbourret.com>]

Tim Bray wrote:
> 
> It's difficult for Matt Fuchs and I to have a straightforward
> discussion because there's some terminology getting in the
> way: Matt calls elements which are in a namespace "global" and
> those which aren't "local".  I suspect that he associates some
> [schema-related?] semantics with the terms "local" and
> "global".

I don't believe Matt is saying this at all. Global and local refer to
the scope of definitions, not identifiers. Furthermore, local element
types can be in a namespace or not, depending on the elementFormDefault
flag.

The problem is actually at the level of definitions. The thinking that
DTDs leads us to and that the namespaces spec reinforces is that an
identifier uniquely identifies an element type and that this element
type has a single definition. This doesn't play well with local element
types, as has already been pointed out.

The problem is that, if a local element type is in a namespace, it can
have the same identifier as another local element type defined
elsewhere. Most reasonable people would say that these are two different
identifiers, but that the namespace spec, which is built on the concept
of universal identifiers, doesn't support this.

In other words, local element types effectively introduce a
per-parent-element-type traditional namespace with which to discriminate
the different local element types, just like local attributes
effectively introduce a per-element-type traditional namespace with
which to discriminate the different local attributes.

Put yet another way, local element types don't play well (at all) with
XML namespaces and contradict one of the fundamental assumptions of the
namespaces specification -- that element types can/should have
universally unique identifiers.

-- Ron