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Re: Minimal dataset semantics

From: Richard Cyganiak <richard@cyganiak.de>
Date: Fri, 24 Aug 2012 12:23:53 +0100
Cc: public-rdf-wg@w3.org
Message-Id: <E88A678B-DEE2-4F37-B90F-1F598DA427C3@cyganiak.de>
To: Antoine Zimmermann <antoine.zimmermann@emse.fr>
On 24 Aug 2012, at 11:48, Antoine Zimmermann wrote:
> Is it the resource denoted by the IRI, or is it the IRI that is associated with the graph?

Please be precise what you mean by "associated".

In the abstract syntax, we have <i,G> pairs. So i and G are paired in a named graph (as per existing SPARQL terminology). Resources do not exist in the abstract syntax.

In the semantics, the pair <i,G> says that the IRI denotes some resource, and that resource has some graph as its graph extension, and that graph entails G.

Or if you want less formal, informative language: In the named graph <i,G>, G is a claim about the state of the resource denoted by i.

> Consider the following, IMHO realistic, example:
> ex:url1 and ex:url2 are the URLs RDF Documents found on the Web. The dafult graph is used to put mappings between different graphs.
> ex:url1  owl:sameAs  ex:url2 .
> ex:url1 { ex:url1  foaf:mbox  <mailto:frank@sinatra.net>}
> ex:url2 { ex:url2  foaf:mbox  <mailto:frank@sinatra.net>}
> (I don't want to hear that this incorrect according to httpRange14. httpRange14 is not part of RDF and, in any case, this example shows something that happens on the Web for real.)

> Now, if it's the resource that is associated with the graph, then we have a resource associated with two graphs. 

Please be precise what you mean by "associated".

In the abstract syntax, we have two different IRIs paired with two different named graphs. No ambiguity.

In the semantics, assuming OWL entailment, the dataset states that ex:url1 and ex:url2 both denote some resource, and that graph has some graph as its graph extension, and that graph entails the two graphs you showed. No ambiguity.

Less formal wording of the semantic situation: We have two named graphs that both make claims about the state of the same resource. The claims don't contradict, so all is fine. No ambiguity.

> Why not, but then it becomes ambiguous when you talk about the graph associated with a resource. Which graph? Do you talk about both graphs all the time.

I never talked about associating graphs with resources. I talked about associating graphs with IRIs, in the sense of "pairing them in a named graph as per existing SPARQL terminology".

> I think that, in conversation, when we say "the graph associated with ex:url1", we tend to mean whatever is in the curly brackets after the IRI rather than an RDF graph that is supposed to be attached to a thing in the world.

I agree.

> We can put IRIs in the interpretation, because IRIs are not only part of the syntax, they are also made part of the semantics by being the literal values of literals with datatype IRI xsd:anyURI.

Yes, but I'm not sure what this has to do with anything.

> Anyway, this idea of having <i,G> pairs in the interpretation should be formalised as it may be a solution that avoids putting several RDF interpretations into one Dataset interpretation.



> --AZ.
> Le 23/08/2012 21:43, Richard Cyganiak a écrit :
>> On 23 Aug 2012, at 19:02, Pat Hayes wrote:
>>>>> b) to define a minimal version of a
>>>>> "truth-based"/"entailment-based" semantics (where [[ :i1 { G }
>>>>> ]] entails [[ :i1 { G' } ]] if graph G entails graph G').
>>> Which means that the "name" refers to the entailment closure of the
>>> graph, rather than the graph itself. Right?
>> I'm not sure what you mean by "refers to".
>> Regarding the formal mechanism of associating IRIs with their
>> respective graphs, I've started to like the idea that Alan mentioned
>> the other day: Dataset interpretations contain a mapping from
>> resources to graphs, called the graph extension. This mapping
>> associates graphs with (some) resources. A name-graph-pair (a.k.a.
>> abstract named graph)<i,G>  satisfies a dataset interpretation I if
>> the graph extension in I of I(i) entails G.
>> If I'm not messing up, then this mechanism works the same as the
>> property extension and class extension mechanisms that already exist
>> in RDF Semantics.
>> So, the graph IRI then *denotes* a resource (one that is in the
>> domain of the class extension function). And in the abstract syntax,
>> the graph IRI is "associated" or "paired" with a certain RDF graph. I
>> don't know if one can say that the IRI "refers to" the entailment
>> closure of the graph.
>> Does this make any sense?
>> Best, Richard
> -- 
> Antoine Zimmermann
> ISCOD / LSTI - Institut Henri Fayol
> École Nationale Supérieure des Mines de Saint-Étienne
> 158 cours Fauriel
> 42023 Saint-Étienne Cedex 2
> France
> Tél:+33(0)4 77 42 66 03
> Fax:+33(0)4 77 42 66 66
> http://zimmer.aprilfoolsreview.com/
Received on Friday, 24 August 2012 11:24:27 UTC

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