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Re: Action 369 -- Look at property path tests

From: Steve Harris <steve.harris@garlik.com>
Date: Tue, 25 Jan 2011 20:46:41 +0000
Cc: Matthew Perry <matthew.perry@oracle.com>, Gregory Williams <greg@evilfunhouse.com>, W3C SPARQL Working Group <public-rdf-dawg@w3.org>
Message-Id: <AC9084D2-A373-4D83-93B2-26C25CEB535D@garlik.com>
To: Andy Seaborne <andy.seaborne@epimorphics.com>
I'm not sure it's any more central than:

?p rdfs:subPropertyOf* ?sp .
:x ?p ?v

and that one wont do what you'd hope, with the current semantics.

- Steve

On 2011-01-25, at 20:36, Andy Seaborne wrote:

> 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
>>> 
>>> 
>>> 
>>> 
>> 
>> 
> 

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Received on Tuesday, 25 January 2011 20:47:17 GMT

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