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Re: putting entailment into SPARQL

From: Pat Hayes <phayes@ihmc.us>
Date: Fri, 16 Dec 2005 09:57:11 -0600
Message-Id: <p06230900bfc8935553fc@[10.100.0.23]>
To: andy.seaborne@hp.com
Cc: "Eric Prud'hommeaux" <eric@w3.org>, RDF Data Access Working Group <public-rdf-dawg@w3.org>

>Pat: specific question:
>
>In 2.7, you suggest text
>
>"""
>Blank nodes in the results of a query are identical to those 
>occurring in the dataset graphs ...
>"""
>
>Not sure about "identical".
>
>A solution matches a basic graph by simple entailment so any bNode 
>in the solution is not necesarily the same as the one corresponding 
>one in the graph.

BUt there is an additional restriction (in the definition of pattern 
solution), that the range of the substitution is a subset of the 
terms actually occurring in the graph. So the answer bindings have to 
be the actual IRIs, literals and bnodes in the graph. (Otherwise 
there could be infinitely many bnodes in answer bindings, and every 
matching query would have infinitely many answers; and without this 
the told-bnode trick wouldnt work.)

>  Together with the document scope of bNode labels in teh XML rsult 
>format and in any RDF serialization, means that even if they were 
>the same, you can't tell.

If there aren't any told bnodes, you can't tell, its true. We still 
need a way to stop bnode-bleeding in the answer bindings, however.

Pat


>  All that is transmitted is whether two bNodes in the document are 
>the same or different.
>
>Or have I missed something?
>
>	Andy
>
>>>
>>>PS. One other rewording in section 2.7:
>>>
>>>"An application or client receiving the results of a query can 
>>>tell that two solutions or two variable bindings differ in blank 
>>>nodes but this information is only scoped to the results as 
>>>defined in "SPARQL Variable Binding Results XML Format" or the 
>>>CONSTRUCT result form."
>>>//
>>>SIMPLE CASE A:
>>>"Blank nodes in the results of a query are identical to those 
>>>occurring in the dataset graphs, but this information cannot be 
>>>used by an application or client which receives these results, 
>>>since all blank nodes in subsequent queries are treated as being 
>>>local to that query. In effect, this means that information about 
>>>co-occurrences of blank nodes may be treated as scoped to the 
>>>results as defined in "SPARQL Variable Binding Results XML Format" 
>>>or the CONSTRUCT result form."
>>>
>>>OR, complex case B with persistent bnodes:
>>>
>>>//"Blank nodes in the results of a query are identical to those 
>>>occurring in the dataset graphs, and may be re-used in subsequent 
>>>queries as persistent blank nodes. Servers which accept a query 
>>>containing a persistent blank node must respect the identity of 
>>>such blank node identifiers across multiple queries and answer 
>>>bindings. In contrast, blank nodes which appear in queries as 
>>>nonpersistent blank nodes are treated as being local to that 
>>>query, and bear no relationship to occurrences of the same blank 
>>>node in other queries or their answer bindings."


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Received on Friday, 16 December 2005 15:57:25 GMT

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