xml-dev - Re: Inheritance and other buzzwords

["Rick Jelliffe" <ricko@allette.com.au>]

From: Tim Bray <tbray@textuality.com>

> The current namespace proposal adds one level of indirection to the names
> we give document components, and includes a technique for ensuring that
> the names are unique across the universe of the Internet.  That's all!


I think Tim is correct in trying to limit people's perception of what the
namespace
proposal does. The basic requirement is, more or less, to have a declaration
which is as simple as possible, as non-intrusive as possible, and which
does not require explicit element or attribute declarations,  which will
allow
the RDF people to say "this element is one of our element types".

Whether there is, underlying this, some more interesting structure of links
derived from type names not instances (my belief), or an underlying
honeycomb of parallel, mutually augmenting schemas (the architectures
idea) should not be the deciding factor for the namespace proposal, to
me. I think it is enough that the namespace 1.0 be expressed in a way that
does not rule out an interpretation using either ot these mechanisms (or
others) is enough at this stage.

It was not Tim's point, but strictly I think the proposal adds two levels of
indirection:
    prefix->ns;   then  ns->schema
It is because of this indirection that the current proposal does not ensure
unique
naming: there is a possibility of an error where two fragments using the
same
prefix are combined under the same namespace declaration. This is
particularly
an issue of maintenance: where a schema is updated, perhaps to make it have
a more restrictive content model.

So XML tools which combine fragments with namspaces will have to be able to
rewrite name prefixes.  If there is
    <?xml:namespace ns="rick" schema="rick-v2-3-1" ?>
and
    <?xml:namespace ns="rick" schema="rick-v2-3-2 ?>
then the processing tool will have to be smart enough to, for example,
relabel
the second PI
    <?xml:namespace ns="rick-a schema="rick-v2-3-2 ?>
and all the names which use this must be relabelled too in the instance.

I believe the net effect of this is that prefixes will begin off simple, and
end up
more and more complex, more and more like partial schema URLs.

Rick Jelliffe


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