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Re: [call for comments] voiD 1.0

From: Simon Reinhardt <simon.reinhardt@koeln.de>
Date: Fri, 30 Jan 2009 10:44:05 +0000
Message-ID: <4982D9F5.2030200@koeln.de>
To: public-lod@w3.org

Peter Ansell wrote:
> What was the rationale behind having both void:target and the
> combination of void:subjectsTarget and void:objectsTarget?
> 
> I would have thought that linksets would always be directed, otherwise
> it leaves you uncertain about whether you can actually find anything
> in one set or the triples are actually contained in the other dataset.
> At least with subjectsTarget you can always be sure that that dataset
> will contain the relevant triples. If people use two void:target
> statements as part of a linkset can we only assume that they are
> trying to include triples from both datasets at once? If so, the
> target's might contain anything resembling the statistics that one
> might be able to apply to directed linksets where one is really only
> trying to describe a subset of triples from void:subjectsTarget that
> happen to have object resources in another known dataset?

void:subjectsTarget doesn't tell you where the interlinking triples are, they will always be contained in the void:Linkset (which you can relate to a void:Dataset via void:subset).
The target properties only tell you in what position of the triple you might find resources from what dataset.
The voiD guide has an example for the use of just void:target instead of the more specific properties [1]: symmetric properties. If you interlink with owl:sameAs for example then the direction doesn't really matter. Another example would be that the resources of the targets might appear in both directions (e.g. DBpedia says that some of its resources are foaf:based_near some GeoNames resources but it also says that some GeoNames resources are foaf:based_near so of its resources).
So if you query a voiD description and you only find void:target properties but no void:subjectsTarget and void:objectsTarget then this tells you that, when querying the linkset itself, you have to expect resources of the dataset you're interested in in both positions. So this would probably affect how you write your SPARQL. Only if the void:linkPredicate is a symmetric property and you know that the dataset does inferencing (taking the symmetry of that property into account!) you can ignore the position. But I don't think you can savely expect a dataset to do such inferencing. :-)

Regards,
  Simon

[1] http://rdfs.org/ns/void-guide#sec_2_2_Directed_vs_Non_directed
Received on Friday, 30 January 2009 10:45:17 UTC

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