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Re: Q to implementers: Resource identifiers - XML Names and/or(concatenated) URIs? (was RE: rdfs.isDefinedBy...)

From: Patrick Stickler <patrick.stickler@nokia.com>
Date: Tue, 11 Jun 2002 10:51:56 +0300
To: "ext Thomas B. Passin" <tpassin@comcast.net>, RDF Interest <www-rdf-interest@w3.org>
Message-ID: <B92B86CC.16786%patrick.stickler@nokia.com>

On 2002-06-10 15:20, "ext Thomas B. Passin" <tpassin@comcast.net> wrote:

> [Patrick Stickler]
>> On 2002-06-09 23:09, "ext Thomas B. Passin" <tpassin@comcast.net> wrote:
>>> There must be only one way to go from URI references to prefixes and
> back
>>> again. That way should be compatible with XML Namespaces.  It should
> always
>>> be possible to use prefixes as aliases for a "base" URI to make it
> easier to
>>> read and write RDF/XML by hand (I say "base" in quotes to distinguish it
>>> from "xml:base", since the two may not turn out to be the same).  After
> all,
>>> it's done all the time in N3, why not everywhere?
>>> Cheers,
>>> Tom P
>> The fact is that qnames and URIs are two competing schemes for global
>> naming, and URIs do not support the structure and contextual semantics
>> defined for qnames -- therefore a fully bidirectional mapping without
>> loss of information is just not possible. URIs will always represent less
>> information than a qname.
>> The solution IMO is for the RDF/XML serialization should be redone in such
>> a manner that *no* qnames are used to denote resources which are denoted
>> by URIs in the graph. I.e., do away with any need to perform a qname<>URI
>> mapping. Resources are ever and only identified with URIs, whether in
>> RDF/XML or the graph.
> I think of this as  a purist's approach and although I can sympathize with
> it, and realize that it is the easiest to get unambiguous, I think there's a
> real place for a capability of useful aliases.

These already exist. They're called ENTITYs. E.g.

   ... rdf:resource="&dc;Creator" ...

In fact, the behavior of XML ENTITYs is identitical to that of RDF's
treatment of qnames. The ENTITY/prefix is simply expanded during
parsing, and has no presence in the resulting graph.

> Seems to me that the
> namespaces ought to be able to work for that.

Namespaces, or rather qnames, will *never* work for that because RDF
disposes of the qname structure and thus usage will always be

Generic round tripping from qname to URI to qname simply cannot work, if
we are to respect the existing standards, which allow Namespaces to be
*any* valid URIRef and which base fragment identifier syntax on the MIME

This is not a purist position. This is a realist position. It just
won't work. Period.

> I do agree with you this far - it ought to be possible to avoid using XML
> namespaces and prefixes in RDF/XML syntax if you want to.

Yes, that would be better than nothing, and would also provide
for a sort of imperfect round-tripping where qnames are mapped
to URIs in the graph and output then only as URIs -- though that
might also lead to alot of user confusion since the input/output
will not be syntactically identical (even though it will be
semantically identical).



Patrick Stickler              Phone: +358 50 483 9453
Senior Research Scientist     Fax:   +358 7180 35409
Nokia Research Center         Email: patrick.stickler@nokia.com
Received on Tuesday, 11 June 2002 04:12:11 UTC

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