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Re: CONSTRUCT operator

From: Pat Hayes <phayes@ihmc.us>
Date: Thu, 26 Jan 2006 14:50:15 -0600
Message-Id: <p06230914bffee5c1b455@[]>
To: tessaris <tessaris@inf.unibz.it>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>

>Pat Hayes wrote:
>>>  Moreover, I think that we should adopt a different notation for the
>>>  variable substitution in graph templates, since it looks the same as
>>>  the one for BGP but it behaves differently. In particular wrt
>>>  variables not present in the domain of a pattern solution.
>>  There once was a tweak in the definition of substitution mapping which I
>>  think handles this, where S(v)=v if v is outside the domain of S, so S
>>  maps V to (RDF_T union V). This makes all S's total on templates and
>>  maps templates to templates (graphs being the special case of templates
>>  with no variables). Would this handle the issue that you are referring
>>  to? (If not, I'd like to see an example, because in that case Im not
>>  following you.)
>It wont take care of the problem, since by the definition in 10.3.2:
>Definition: Graph Template
>A graph template is a set of triple patterns.
>If T = { t_j | j = 1,2 ... m } is a graph template and S is a solution
>then S(t_j) is a set of one RDF triple if all variables in t_j are in
>the domain of S. S(t_j) is the empty set otherwise.
>Write S(T) for the union of S(t_j).
>triples with variables without assignment "disappear"; while mapping the
>variables into themselves would generate an RDF graph with variables.

Ah, now I see what the problem is that you were referring to. OK.



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Received on Thursday, 26 January 2006 20:50:29 UTC

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