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Blank nodes and predicates

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Mon, 30 Jan 2006 11:28:26 +0000
Message-ID: <43DDF85A.8020804@hp.com>
To: RDF Data Access Working Group <public-rdf-dawg@w3.org>

At the moment, rq23 allows blank nodes in the predicate position both in the 
definition of a triple pattern and in the grammar.  I changed the definition 
recently to make the syntax and the definitions consistent.  There are 
approved syntax tests with bnodes in the predicate position but, being syntax 
tests, the tests do not given any clue as to what is supposed to happen.

The text in 2.5.2 that describes how to do simple entailment matching would 
cover the case of blank nodes in the predicate position.  Pat said in the 
telecon (26 jan 06) that a blank node in the predicate position would never 
match under entailment.

Looking for experience, I tried cwm.  cwm allows blank nodes in the predicate 
position in rule matching.

I tried --

@prefix : <http://example/> .
:x :p 1 .
{ ?x _:p 1  } => { ?x :q 2 } .

and got :x :q 2 . in the resulting graph.

I have added this as a test case in tests/data/BasicGraphPatterns
http://www.w3.org/2001/sw/DataAccess/tests/data/BasicGraphPatterns/

We need to be consistent: if they can match then we can allow them in both 
syntax and definition of a triple pattern.  If they don't, then I see it as 
confusing to allow them in the syntax or definition of triple pattern.

	Andy
Received on Monday, 30 January 2006 11:29:55 GMT

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