Namespaces and URNs
peter at ursus.demon.co.uk
Tue Aug 4 20:32:48 BST 1998
I would appreciate guidance from people knowledgeable in URN syntax and use.
(A) The NS draft gives an example as
but a private correspondent tells me than URNs should be of the form
urn:scheme:something - so unless loc.gov is a scheme there appear to be
differences of opinion.
(B). I would greatly value consistency in the use of standard URNs. The
only way we can implement interoperability is if everyone uses the same URN
to refer to a namespace. Since the URN need not represent a real WWW
resource there is very little check on whether a URN is fictitious.
The draft shows an example of this problem. HTML is referenced mainly
through the string:
This seems fine to me, but later (5, box 6) it is referenced by:
Are these equivalent? If so, there must be a central registry of synonyms
somewhere. And, if so, it places a great burden on implementers who must
search the WWW for all possible equivalences. I would *much* prefer that
the whole world used exactly the same string for the namespace for HTML4.0.
Experience with HTML has not helped the cause of unique identifiers for
DTDs. I suspect that there are zillions of different (F)PIs in the HTML
DOCTYPE statements round the world. And - unless I'm told different - I
suspect no software actually processed them. So we are going into an era
where we have to convince authors that NS URNs are critically important -
they can't just guess and hope.
I'd like to suggest that people who really know post the authoritative
URNs for common DTDs/schemas. And that we all stick to using the correct
one in all our examples. Among the ones we shall need in many namespace
HTML (including version)
MathML (a useful example)
Having developed 2 DTDs (CML and VHG) I need to know how to prepare URNs
for them. It seems clear that anyone wishing to create a DTD which can be
used for Namespaces has to buy/borrow a domain name. (I suppose they could
buy an FPI instead, but since I already have domain names I'd prefer to
stick with those).
Peter Murray-Rust, Director Virtual School of Molecular Sciences, domestic
VSMS http://www.nottingham.ac.uk/vsms, Virtual Hyperglossary
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