W3C home > Mailing lists > Public > public-rdf-dawg@w3.org > April to June 2011

ACTION-418: review property paths section in Entailment

From: Axel Polleres <axel.polleres@deri.org>
Date: Wed, 20 Apr 2011 00:40:32 +0100
Message-Id: <71C5F859-D155-4CFE-8CB3-591AE2BE9A0B@deri.org>
To: SPARQL Working Group <public-rdf-dawg@w3.org>, Birte Glimm <birte.glimm@comlab.ox.ac.uk>
1) Editorial:

"In the presence of entailment path expressions are sometimes redundant as their semantics is already captured by the entailment relation."
-->
"In the presence of a particular entailment regime, path expressions are sometimes redundant as their semantics is already captured by the entailment relation."

2) Editorial. THe simplified version of the query:

 "SELECT ?type ?c WHERE { ex:a rdf:type ?x . { ?x rdfs:subClassOf{0} ?type } UNION { ?x rdfs:subClassOf+ ?type } ex:a ex:p1 ?tmp1 . ?tmp1 ex:p2 ?c }"

should be:

 "SELECT ?type ?c WHERE { ex:a rdf:type ?x . { ?x rdfs:subClassOf{0} ?type } UNION { ?x rdfs:subClassOf+ ?type } ex:a ex:p1 ?tmp1 . ?tmp1 ex:p3 ?c }"

likewise
  "bgp2 = ex:a ex:p1 ?tmp1 . ?tmp1 ex:p2 ?c"

should be 
  bgp2 = ex:a ex:p1 ?tmp1 . ?tmp1 ex:p3 ?c"

 likewise
  "Evaluating Bgp(ex:a ex:p1 ?tmp1 . ?tmp1 ex:p2 ?c) would yield [...]"
should be 
  Evaluating Bgp(ex:a ex:p1 ?tmp1 . ?tmp1 ex:p3 ?c) would yield [...]"

shouldn't it? i.e. s/ex:p2/ex:p3/

                                            
3) Question (potentially problematic):  On your example data which includes the triples

     ex:b ex:p2 ex:c .
     ex:p2 rdfs:subPropertyOf ex:p3 .
 
   Would the query
      Q  =  SELECT * WHERE { ?X (ex:p3+) ?Y }
   yield any results? 

It seems no: If I read it correctly, since ArbitraryPathLength is checked without taking entailments into account, so it wouldn't "catch" that p3 is a 
superproperty of p2 in this form, would it? However, a result might be expected for that query under RDFS.

An implementation the implememnts RDFS by materialising all inferences and then running normal SPARQL evaluation would yield a different result, 
as far as I can tell, and that should be pointed out. Ideally we don't lock-in into that, i.e. we should at least keep a path open that 
future entailment regimes can  address path expressions in a more intuitive way, but I'm not sure at the moment how that could be done.

If the observation is right, then I am also unsure about the last sentence "Combining the other entailment regimes with property path expressions is, however, relatively straightforward." since people might not find the result of Q very straightforward.


best,
Axel

     
Received on Tuesday, 19 April 2011 23:41:02 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 16:15:46 GMT