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Re: RDF Issue rdfms-literalsubjects

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Sun, 24 Feb 2002 19:28:49 -0600
Message-Id: <p0510144bb89f42339ce4@[65.212.118.219]>
To: "Seth Russell" <seth@robustai.net>
Cc: www-rdf-comments@w3.org
>From: "Tim Berners-Lee" <timbl@w3.org>
>
>[[
>I understand that current RDF does not allow subjects to be literals. This
>is acceptable as a response at this stage, because of the damage to the RDF
>syntax to try to fix it.
>]]
>
>I don't understand this "damage" to syntax.  What are the problems with just
>using something like "rdf:aboutLiteral" instead of "rdf:about" where the
>subject is a literal?   I gather that there is no problems with the
>semantics of using literals for subjects.

There are some syntax issues. One problem arises as follows. Imagine 
that we allow literals as subjects, and we have the following kind of 
situation

aaa --ppp---> "13" ---qqq---> bbb

ccc --rrr-->"13" ---sss--> ddd

Now if we have 'tidy' literals - which many people want to, for 
technical reasons - then those two literals have to be the same node; 
and then we have a graph with five nodes consisting of a literal with 
two triples coming 'into' it and two triples coming 'out of' it, but 
no way to tell which goes with what. If these were blank nodes we 
could just use two nodes, but the literal labels will *force* the 
nodes to be merged (if nodes are tidy).

Im not saying this would be fatal, but it would create some new 
problems. And there are also some issues with using the Ntriples 
syntax with literals as subjects. And, of course, XML introduces yet 
more syntactic conditions. So one way and another, it is a bit of a 
mare's nest.

Pat

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Received on Sunday, 24 February 2002 20:28:57 GMT

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