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Re: Test cases and examples for dataset entailment

From: Antoine Zimmermann <antoine.zimmermann@emse.fr>
Date: Tue, 11 Sep 2012 23:11:46 +0200
Message-ID: <504FA912.70309@emse.fr>
To: Richard Cyganiak <richard@cyganiak.de>
CC: public-rdf-wg@w3.org
Le 11/09/2012 19:46, Richard Cyganiak a écrit :
> On 11 Sep 2012, at 14:37, Antoine Zimmermann wrote:

[skip]

>
>> However, people who are interested in implementing support for the
>> vocabulary can interpret the terms in a special way. People already
>> do that. There are tools that display instances of foaf:Person in a
>> special way. There are Web crawlers that interpret the voiD
>> vocabulary in a special way. They do not need that the special
>> interpretation be hard coded in reasoners.
>
> I don't know what your point is. A semantic extension is not a
> requirement for hard coding anything in a reasoner.

I realise that we, and others, may not have the same idea of what a 
proper semantic restriction is. For me, a semantic restriction is, for 
instance, what RDFS is to RDF, what D-entailment is to RDFS and what OWL 
Full is to D-entailment.

If you want to implement RDFS semantics, you have to hard code the 
entailment, consistency check and such things in a reasoner.

With the direct graph semantics you propose, it is a non-monotonic 
extension because when you switch this semantics on, the entailments you 
could do with the "minimal" semantics are not valid anymore. I don't 
think that's how people think of an extension. They probably do not 
expect that extensions make you lose what you had before.
It also means that people who do not use the extension get conclusions 
contradicting those who use the extension. This is not the case with 
RDFS, OWL, etc. If you do not use D-entailment, you are not going to get 
any conclusions that contradicts those who use it. And those who switch 
the D-entailment semantics on do not lose anything they could conclude 
without it.

I understand that you wrote this merely as an example, and it indeed 
proves that such semantics can be defined as a semantic extension of our 
"minimal" proposal. I provided similar things myself already [1]. But 
even when I was writing this, I was not convinced by the utility. I only 
used it as a proof that it can be done, formally.


[1] http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs/Dataset-semantics

--AZ

>
>> If I had to directly talk about a graph in a named graph, I would
>> do it like this:
>>
>> :g  a  sd:Graph; :validityTime  "1998-09-11"^^xsd:date; ... :g  {
>> :bob  :employedBy  :ibm }
>>
>> It works, as long as I am using an agreed upon, explicit
>> specification of a shared conceptualisation, a.k.a. an ontology.
>
> Yeah, and that's exactly the example I gave, except I called it
> rdf:Graph instead of sd:Graph, and formalized the implicit assumption
> that :g actually denotes { :bob :employedBy :ibm } as opposed to some
> other graph. You can't do that just by defining an ontology.
>
> The benefit of formalizing this is that, for example, if I define a
> Turtle datatype then it will just work, and I can infer
>
> { :g owl:sameAs ":bob :employedBy :ibm"^^xxx:Turtle }
>
> from the dataset above, modulo namespace declaration.
>
> Best, Richard
>
>
>
>
>>
>>
>> AZ.
>>
>>
>>
>>
>> Le 11/09/2012 11:46, Richard Cyganiak a écrit :
>>> On 10 Sep 2012, at 17:30, Richard Cyganiak wrote:
>>>> Two other things that I'd quite like to see before we can call
>>>> the proposal complete:
>>>>
>>>> 1. Some thinking on how it addresses our graph use cases. (Do
>>>> we have an “official” list of those? I've lost track with all
>>>> the various documents.)
>>>>
>>>> 2. Some examples for semantic extensions, in order to show that
>>>> various other proposed semantics can actually be done as proper
>>>> semantic extensions of this minimal dataset semantics.
>>>
>>> I've worked a bit on this item and made attempts to formalize
>>> three semantic extensions:
>>>
>>> * owl:imports (formally explains how owl:imports works in RDF
>>> datasets) * web datasets (formally defines that stuff published
>>> on the web is asserted) * direct graph semantics (permits
>>> "literal" immutable graphs)
>>>
>>> http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs/Minimal-dataset-semantics#Possible_Semantic_Extensions
>>>
>>>
>>>
I'm not proposing that we should standardize any of this; the intention 
is merely to explore how flexible/extensible the semantics proposed on 
that page is.
>>>
>>> Again, I'm not really good at this formal semantics stuff, so
>>> this might all be spectacularly wrong.
>>>
>>> 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/
>>
>
>


-- 
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 83 36
Fax:+33(0)4 77 42 66 66
http://zimmer.aprilfoolsreview.com/
Received on Tuesday, 11 September 2012 21:12:47 GMT

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