Inheritance and other buzzwords

[Rick Jelliffe]

From: james anderson <James.Anderson at mecom.mixx.de>

> there were some things in a remark yesterday from Rick Jelliffe and in a
note
> from Peter Murray-Rust which lead me to doubt that wd-xml-names will work
unless
> it is extended to more completely specify the semantics of the namespace
> declaration pi.


I think the wd-namespace will work as advertised, but I think a lot of
people
will try to use it for more than the uses that it pupports to address.
Following are
some general comments.

> in previous remarks, it has been explained that the wd expressly avoids
> specifying a semantics.

1) Some people claim that the difference between a hyperlink and an entity
declaration/reference is that there is something voluntary or contingent
about a hyperlink while an entity declaration/reference expresses a
more fixed and necessary relationship.  If we accept that for a second,
then I think Andrew's comments are clearer: the schema nominated
in the namespace declaration is not "specified" rather it is "identified".

So namespace PI is more like a hypertext link rather than an entity
reference.

Some people think that, in the long run, document-specific
type structures will be declared (using XML-data or XML markup
declarations) in the document, while external-vocabulary schema
fragments will be defined externally, invoked using the namspace PI.
(I think it is more likely that names borrowed from HTML schema
will be unprefixed, while all others will be.)

In that case, namespace PIs act more like a kind external entity
reference--more like the ISO "module" proposal.

2) I think the term "scope" shouldn't be used here: all namespace PIs have
scope over the entire document, not over particular entities. And an element
type name without a prefix has no binding to a schema using the namespace
mechanism (it still could use the standard XML markup declarations, or
architectural forms, or ICADD fixed attributes, or other home-made systems
though.)

3) My point about namespace PIs having the same prefix is merely that
without the namespace PI there is the possibility of a clash with every
name.
The namespace PI does not guarantee name uniqueness accross all
documents,  it merely decreases the number of clashes. This is pretty weak
in my book, but it is workable provided developers understand it and
write their software accordingly.

With the wd-namespace PI the number of possible things that can clash
is reduced to the prefixes themselves and to unqualified names.  And the
prefixes give corporate and project names, not common element names:
it is very easy to predict that two documents will have incomptible element
types named "table", not so many documents will have incompatible
namespaces called "rdf" (except for the versioning issue mentioned
previously).

Of course, it would be much better to have "w3.org-rdf" as the prefix, since
that would introduce some discipline. Certainly if I ever use namespace PIs
I would try to make sure that my prefix had some robustness to it, by
including an organization name in it.

Rick Jelliffe


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