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Re: Final text for Basic Graph Patterns

From: Enrico Franconi <franconi@inf.unibz.it>
Date: Tue, 17 Jan 2006 18:03:15 +0100
Message-Id: <AA396E67-60E0-475D-A4D0-7D97352C98DA@inf.unibz.it>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>
To: Pat Hayes <phayes@ihmc.us>

A quick reaction:

On 17 Jan 2006, at 17:42, Pat Hayes wrote:

> Enrico Franconi wrote:
>
>> The new proposal of Pat <http://lists.w3.org/Archives/Public/ 
>> public-rdf-dawg/2006JanMar/0061.html> does not work for any  
>> approach where bnodes are implicit, and this happens not only for  
>> OWL-Lite entailment, as we already pointed out in <http:// 
>> lists.w3.org/Archives/Public/public-rdf-dawg/2006JanMar/ 
>> 0064.html>, but also for RDF entailment. For example, given the graph
>>     :john :age "25"^^xsd:decimal .
>> the query
>>     ASK { _:b rdf:type rdf:XMLLiteral }
>> should clearly return YES if RDF entailment is considered.
>
> I agree, and see below.
>
>> However,
>> according to the latest proposal from Pat the answer to the query  
>> would be NO regardless of the type of entailment considered. The  
>> reason is that Pat considers bnodes in the query restricted to be  
>> bound only to URIs and bnodes explicitly appearing in the graph.
>
> This restriction is to terms occurring in the scoping graph, not in  
> the original graph. For the SPARQL case of simple entailment, the  
> scoping graph is defined to be equivalent to the dataset graph, but  
> for  RDF or RDFS entailment, the appropriate adjustment would be to  
> define the scoping graph G' to be the RDF or RDFS closure of the  
> data set graph G.

Oh, no. We are not going through the graph closure discussion again.
The decision to have entailment was exactly to replace the closure of  
the graph.
Your proposal does not scale up: the closure of an RDF (or RDFS)  
graph is infinite, and the closure of a OWL-DL graph is not unique  
(OWL-disjunction).
Moreover, if you let the scoping graph G' in the definition of basic  
graph pattern matching, the algebraic expressions involving more than  
one BGP wouldn't work properly (since you can not control whether  
there are distinct scoping graphs Gi').
Full stop. Unacceptable by FUB.

As we already pointed out, if you really want a scoping graph G',  
this should appear once forever outside the definition of basic graph  
pattern matching, most likely at the beginning of any processing of  
the original graph G by the SPARQL server. But probably, most of your  
arguments wouldn't make anymore sense if this is just a pre- 
processing operation.

cheers
--e.
Received on Tuesday, 17 January 2006 17:03:25 GMT

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