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Re: Review SPARQL Query 1.1, Section 18 (algebra)

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Mon, 21 Mar 2011 10:50:18 +0000
Message-ID: <4D872D6A.6070006@epimorphics.com>
To: Birte Glimm <birte.glimm@comlab.ox.ac.uk>
CC: SPARQL Working Group <public-rdf-dawg@w3.org>


On 15/03/11 00:34, Birte Glimm wrote:
> 18.6
> The overall SPARQL design can be used for queries which assume a more
> elaborate form of entailment than simple entailment, by re-writing the
> matching conditions for basic graph patterns.
>
> This is no longer true due to PPEs. I am not happy about this at all
> and I assumed that PPEs are optional features. If they are not, it is
> quite unfortunate that the so far existing extension point no longer
> really is one and something has to be done at least to clarify this!

Property paths are handled by maximising the rewrites to other SPARQL 
forms, including BGPs, and introducing new SPARQL algebra operators only 
where necessary.

Therefore, evaluation of property paths does reduce to algebra+BGPs, 
just like any SPARQL query pattern.

Would it be useful for the entailment document to discuss the issue that 
the property path syntax is compiled to SPARQL algebra forms.  It would 
be useful to discuss the relationship of applications-defined 
relationships (which is what property paths do - give the application 
writer a chance to express complex relationships such as transitivity) 
and the ontology-defined relationships that manifest via entailment. 
This might include limitations on the patterns in the syntax although 
that weakens the expressivity otherwise given to the application query 
writer.

	Andy
Received on Monday, 21 March 2011 10:50:54 GMT

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