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Re: Really minimal dataset semantics

From: Antoine Zimmermann <antoine.zimmermann@emse.fr>
Date: Fri, 21 Sep 2012 17:33:22 +0200
Message-ID: <505C88C2.9050101@emse.fr>
To: "Peter F. Patel-Schneider" <pfpschneider@gmail.com>
CC: public-rdf-wg <public-rdf-wg@w3.org>
Le 21/09/2012 17:25, Peter F. Patel-Schneider a écrit :
>
> On 09/20/2012 12:00 PM, Antoine Zimmermann wrote:
>> Le 20/09/2012 16:54, Peter F. Patel-Schneider a écrit :
>>>

[skip]

>>>
>>> In the semantics there is no notion of a relationship between a name and
>>> an actual graph.
>>
>> In the semantics to which I refer (viz., first version of the Minimal
>> dataset semantics) there is a function IGEXT that maps graph IRIs to RDF
>> graphs. Isn't this a notion of a relationship between a name and an
>> actual
>> graph?
> No, as it does not distinguish between equivalent graphs. Suppose you
> have two equivalent graphs, then you can use them interchangeably in
> your semantics.

If I have 2 equivalent graphs, I can use them interchangeably according 
to the *RDF semantics*. It's not my fault.


>> Or maybe, by "actual graph", you mean a graph that is actually
>> "written" in
>> a given dataset? Normally, the semantics defines the notion of
>> interpretation independently of a given formula, and an interpretation
>> makes
>> true all sorts of formulas.
>>
>> In what I propose, for an interpretation to make a named graph true, the
>> name has to be related (via IGEXT) to whatever graph makes the graph
>> inside
>> the pair true.
>>
> Yes, but this doesn't pick out the actual graph, just one of many
> possible graphs.

If you want the graph inside a <name,graph> pair, just read the dataset. 
There are APIs for this.

Dataset d = loadDatasetFromFile(new File("foo.trig"));
Graph g = d.getGraph("http://ex.com/g");

That's it.

>>
>>> 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?
>>
>> By IGEXT, it does, but a dataset interpretation is not defined in
>> function
>> of a given dataset, so there is no reason that the name be associated
>> with
>> the "actual graph" in a given dataset.
>
> Why not? Isn't a major use case for RDF graphs to record where graphs
> (actual graphs, not equivalence classes of graphs) come from?

And what's this has to do with semantics?
If I want to record someone's speach, I don't need to know the semantics 
of what he/she says.


>>>
>>> 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.
>>
>> Sorry, maybe I misunderstood what you were saying, but then I don't
>> understand your point.
>>
>> What I'm saying is that, if you find a dataset somewhere in the wild,
>> or if
>> you have a dataset in memory, you can get the graph associated with a
>> graph
>> IRI by simply parsing the dataset representation. Semantics does not come
>> into play in that case.
>>
>>
>> --AZ
>
> Sure, you can look right in the dataset to find the graph, no semantics
> involved. However, if RDF datasets is supposed to be able to carry some
> meaning about graphs and their sources then shouldn't its semantics
> actually use graphs?

No, they are not supposed to carry information about the graph. That's 
only one use case, and we know there are people against this idea (e.g., 
the default as merge case). I want the common denominator that would not 
lead to erroneous entailments according to anybody's understanding of 
datasets.

For metadata about graphs, provenance, dates, whatever, define a 
vocabulary and make sure that all applications that support the 
vocabulary interpret it in the same way. It has been done before and it 
works.


AZ

>
> peter
>
>

-- 
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, 21 September 2012 15:33:54 GMT

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