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Tidy literal nodes incompatable with current MT?

From: Patrick Stickler <patrick.stickler@nokia.com>
Date: Mon, 28 Jan 2002 13:28:35 +0200
To: RDF Core <w3c-rdfcore-wg@w3.org>
Message-ID: <B87B0283.C6F7%patrick.stickler@nokia.com>

It has occurred to me that tidy literal nodes seem incompatable
with the view that a node in the graph maps to one and only one
thing in the universe.

The reason why URI labeled nodes can be tidy is because URIs
are globally unique, and URIs are presumed to have a consistent
global meaning. But literals are like local names, and their
meaning is dependent on context. Literals do not have a consistent
global meaning.

If two literals which have different interpretations are
denoted by a single node, then that node maps to more than
one thing in the universe, and N:N mappings between resources
to things introduces an unacceptable ambiguity into RDF.

I agree that it is desirable, from an implementation viewpoint,
to be able to compress literal value nodes if possible, and
that is what URVs are for -- to encapsulate the TDL pairing
of lexical form and datatype identity into a single globally
unique resource that can participate in node tidying.

Thus, while the literal nodes with label "30" in

   Bob foo:jerseyNumber "30" .
   Jane ex:age "30" .
   foo:jerseyNumber rdfs:range foo:count .
   ex:age rdfs:range xsd:integer .

can never be tidied because they have different interpretations,
one could use tdl: URVs to achieve a significant degree
of compression

   Bob foo:jerseyNumber <tdl:(foo:count)30> .
   Jane ex:age <tdl:(xsd:integer)30> .

(forgive the use of qnames in the above tdl: URIs...)
 
where the value nodes, now having URI labels, can participate
in tidying, and all occurrences of <tdl:(foo:count)30>
are merged to the same node, and that node has a globally
consistent interpretation, and likewise all occurrences
of <tdl:(xsd:integer)30> are merged to the same node, again
having a globally consistent interpretation.

C.f.

http://ietf.org/internet-drafts/draft-pstickler-tdl-00.txt

--

So, in conclusion, while TDL is agnostic about tidy versus
untidy literal nodes insofar as interpretation is concerned,
it does not appear that tidy literal nodes is compatable with
the present MT and the presumed N:1 mapping from nodes in
the graph to things in the universe (anyone feel free to set
me straight if I'm mistaken about that presumption).

Patrick

--
               
Patrick Stickler              Phone: +358 50 483 9453
Senior Research Scientist     Fax:   +358 7180 35409
Nokia Research Center         Email: patrick.stickler@nokia.com
Received on Monday, 28 January 2002 06:27:32 EST

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