Namespaces and URNs

Peter Murray-Rust peter at
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 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
examples are:
	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
net connection
VSMS, Virtual Hyperglossary

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