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Re: Action 369 -- Look at property path tests

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Tue, 25 Jan 2011 20:36:26 +0000
Message-ID: <4D3F344A.1010001@epimorphics.com>
To: Matthew Perry <matthew.perry@oracle.com>
CC: Gregory Williams <greg@evilfunhouse.com>, W3C SPARQL Working Group <public-rdf-dawg@w3.org>
The "?x :p{0} :const" case comes from:

data:
:x :prop 123 .

Query
{
   ?p rdfs:subPropertyOf* :prop .
   :x ?p ?v .
}

properties aren't nodes (vertices = subject/objects) in the graph.

Other than that, we could make { ?x :p{0} "o" } test on graph nodes 
(vertices), but this one is rather central to the semantic web.

	Andy

On 25/01/11 16:53, Matthew Perry wrote:
> It seems strange to me to get any results with an empty dataset. I don't
> agree that terms from the query should be included in nodes(G). From my
> understanding, { ?x ?p "o" } will not match if "o" does not appear in
> the dataset, so I don't think { ?x :p{0} "o" } should match.
>
> - Matt
>
> On 1/25/2011 11:16 AM, Gregory Williams wrote:
>> On Jan 25, 2011, at 9:41 AM, Matthew Perry wrote:
>>
>>> I have reviewed the property path tests. We need tests for {m,n},
>>> {,n}, ? and () for precedence, and I think we need more tests for
>>> combinations of property path constructs.
>>>
>>> I have disagreements with some of the answers given in the current
>>> tests.
>>>
>>> 1) pp15 -- I don't see why we are returning results on an empty dataset.
>> pp15 returns results because zero-length property paths bind the path
>> endpoints to any subjects or objects in the graph *and* any bound term
>> explicitly in the query. So in pp15, ?X :p{0} "o" will bind ?X="o".
>> Likewise for ?Y and ?Z. This is part of the evaluation semantics for
>> ZeroLengthPath
>> (http://www.w3.org/2009/sparql/docs/query-1.1/rq25.xml#sparqlAlgebraEval),
>> though maybe it could be made clearer in the description of property
>> paths in section 9 (from the evaluation semantics, I take "graph node"
>> in section 9 to include terms not necessarily in the dataset but that
>> are present in the query).
>>
>> .greg
>>
>>
>>
>>
>
>
Received on Tuesday, 25 January 2011 20:37:08 GMT

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