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problems with simple entailment rules

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Sun, 03 Aug 2003 08:48:15 -0400 (EDT)
Message-Id: <20030803.084815.39017339.pfps@research.bell-labs.com>
To: www-rdf-comments@w3.org

I believe that there is a problem with the definition of ``allocated to''
in the simple entailment rules.  The definition currently (as of the 31
July version) states

	The terminology 'allocated to' means that the blank node much have
	been created by an earlier appliation of the specified rules on the
	same URI reference or literal, or if there is no such blank node
	then it must be a 'new' node which does not occur in the graph.

My reading of this is that the following RDF graph

	<ex:a> <ex:p> <ex:b> .

cannot be expanded to 

	<ex:a> <ex:p> <ex:b> .
	<ex:a> <ex:p> _:a .
	<ex:a> <ex:p> _:b .

using the simple entailment rules because once there is a blank node
created from <ex:b> then all subsequent rule applications must use that
blank node for <ex:b>.

Also

	<ex:a> <ex:p> _:a .

cannot be expanded to 

	<ex:a> <ex:p> _:a .
	<ex:a> <ex:p> _:b .

because se1 requires that the object of the triple be a URI reference or
literal.  

This means that the simple entailment rules are not a replacement for the
instance relationship, which counters the claim in Section 7.1.  Nor are
the simple entailment rules complete for simple entailment, which, by the
way, is not stated in the document.

Nor are the simple entailment rules equivalent to the alternative rule
formulation in the second-last paragraph of Section 7.1, as this
alternative formulation admits the first expansion above.  Nor is this
alternative rule formulation a replacement for the instance relationship,
as it does not admit the second expansion above.

Peter F. Patel-Schneider
Bell Labs Research
Lucent Technologies
Received on Sunday, 3 August 2003 08:48:23 GMT

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