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Re: [SKOS, SPARQL, ALL] Closure and SPARQL

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 12 Dec 2005 12:01:43 -0600
Message-Id: <p0623090dbfc36aefd834@[10.100.0.23]>
To: Enrico Franconi <franconi@inf.unibz.it>
Cc: <public-swbp-wg@w3.org>

>On 12 Dec 2005, at 11:49, Christoffel Dhaen wrote:
>>Thatıs all. RDF is a graph, it has native 
>>transitive properties. Being able to express in 
>>query that only the direct nodes should be 
>>taken into account, or that the transitive 
>>nature of the properties has to be taken into 
>>account is a logical step. No more, no less.
>
>At this point it is not clear to me anymore what you want :-)
>
>1) if you want, e.g., to ask for the 
>"descendant" property if you have only the 
>"child" property in the graph, then you need the 
>abiltiy to express the transitive closure of a 
>property in the query language. This has a cost, 
>and current SPARQL does not handle this.
>
>2) if you want to distinguish in a query between 
>"stated" transitive properties from "derived" 
>transitive properties, then you need a different 
>mechanism. This would be the case of existing 
>transitive properties in RDFS; e.g., subClass: 
>if there is a graph "(a subClass b)(b subClass 
>c)" whenever you ask for "(X subClass c)" you 
>want to get the answer "X=b" as being somehow 
>directly stated as opposed to the answer "X=a" 
>as being somehow derived. This distinction is 
>possible according to the latest discussions in 
>the DAWG: if you make the query "(X subClass c)" 
>by requiring only "simple RDf entailment" you 
>get the answer set {X=b}, while if you require 
>"RDF entailment" you get the answer set {X=b, 
>X=a}.

Actually you need RDFS entailment to get this, 
but I agree with your basic point.

(RDF entailment just gets you the XMLLiteral 
datatype and type-checking of properties, so that 
if you query
?X rdf:type rdf:Property
you will get back all the property labels in the graph.)

>"simple RDf entailment" and "RDf entailment" are 
>defined in the RDF MT semantics W3C document.
>
>Does this characterise your request?
>
>cheers
>--e.


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Received on Monday, 12 December 2005 18:01:56 UTC

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