- From: Pat Hayes <phayes@ihmc.us>
- Date: Thu, 26 Jan 2006 14:50:15 -0600
- 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.
Pat
>--sergio
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Received on Thursday, 26 January 2006 20:50:29 UTC