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Re: Really minimal dataset semantics

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Thu, 20 Sep 2012 10:54:41 -0400
Message-ID: <505B2E31.4040806@gmail.com>
To: Antoine Zimmermann <antoine.zimmermann@emse.fr>
CC: Pat Hayes <phayes@ihmc.us>, RDF WG <public-rdf-wg@w3.org>

On 09/20/2012 05:49 AM, Antoine Zimmermann wrote:
> Le 19/09/2012 22:12, Peter F. Patel-Schneider a écrit :
>> I also have problems with any dataset semantics that isn't based on the
>> actual form of the named graphs.
> I don't understand this.
>>   Isn't a major use of datasets
>> supposed to be for associating a graph with its source?
> Sure. This type of use case is compatible with the semantics.
>>  if so, neither
>> of these two semantics seems to be correct, as the meaning of a named
>> graph in a dataset is not a graph but is instead something like an
>> equivalence class of graphs.
> I don't understand. Where do you see equivalence classes?

Interpretations for named graphs talk directly about entailment.  If you 
change an interpretation by replacing a named graph with an equivalent one, 
then the truth values don't change.
>>  The semantics then destroys the
>> relationship between the name and the actual graph.
> It does not destroy anything because a semantics does not *do* anything. The 
> actual relationship between the name and the actual graph is written in the 
> dataset.
> You could argue along these lines saying that the RDF semantics destroys the 
> relationship between the property names and the actual pairs 
> (subject,object) that are actually in the graph.
> If you want to know what subjects or objects occur with a predicate inside a 
> graph, just look at the graph. There are APIs for this.
> Same for datasets.

In the semantics there is no notion of a relationship between a name and an 
actual graph.

If named graphs and RDF datasets are supposed to carry a relationship between 
a name and an actual graph, then shouldn't the semantics reflect this?

This is totally different from properties.  No one should be arguing that RDF 
graphs are supposed to carry a relationship between a name and a set of 
pairs.  Instead this is what the semantics does.

>  (Of course, you
>> could always just ignore the semantics and directly use the graph from
>> the dataset, but then what is the point of having the named graph there?)
> The data structure is also very important, just as in RDF graphs, the data 
> structure is already a nice way of organising the data, linking data 
> together, etc. Semantics does not have to come into play where it has no role.
> --AZ

Huh?  If the meaning of a named graph is tied up with relating names to 
graphs, then the semantics certainly has a role there.

Received on Thursday, 20 September 2012 14:55:18 UTC

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