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[RIF-RDF-OWL/Core] ## vs. rdfs:subClassOf (Fwd: A technical RIF question)

From: Axel Polleres <axel.polleres@deri.org>
Date: Thu, 25 Feb 2010 10:02:09 +0000
To: RIF <public-rif-wg@w3.org>
Message-Id: <B39F4145-3BCB-46DB-97B3-E02837165147@deri.org>
Hi all,

Ivan raised the question why ## was not in RIF Core... I tried to exploit my memories on this as good as I can, but I am not 100% sure whether I got everything right and would seek confirmation of the group. Also, there's a small issue which I don't like and want to raise here...


since from the mails below, the thread may be hard to grasp, let me summarise:

Ivan asked for the reason of the absence of ## in RIF Core - in the context of modelling rdfs:subclassOf .
I didn't really remember precisely the details why we dropped ## from Core, but pointed Ivan to the difference 
between ## and rdfs:subclassOf , that is, ## not being reflexive.

However, what then still worried me a bit is following:
Note that http://www.w3.org/TR/rif-rdf-owl/ restricts RDF-OWL interpretations 
in such a way that ## implies rdfs:subclass but not the other way around.
The Embedding of RIF combinations in Section 9.1.3 of
http://www.w3.org/TR/rif-rdf-owl/ enforces this by a rule... which then makes even the 
embedding of simple RDF entailment go outside RIF Core... I am not sure whether I like this. :-|

Ivan, suspected even a "bug" here, by the assumption that if I talk about simple and RDF interpretations,
I shouldn't worry about the RDFS vocabulary, but I wouldn't go that far:

As far as I can see, this is not problematic. We just restrict that when you throw RIF and RDF stuff together,
a link is made from ## to rdf:subclasss... that implies that anything which is stated as ## in RIF is 
exported to rdfs:subclassOf (but NOT the other way around!) only in RIF-RDFS-entailment this would have 
cross-effects (since RDFS interpretations imply reflexivity on rdfs:subclass), but not in RIF-Simple and RIF-RDF.

Still, and here I think Ivan's concern plays a role, I don't like that now for embedding simple 
RDF or RDF in RIF, I need non-core rules... in fact, it seems to me that the rule
in Section 9.1.3 of http://www.w3.org/TR/rif-rdf-owl/ 

 Forall ?x ?y (?x[rdfs:subClassOf -> ?y] :- ?x ## ?y]) ))

is irrelevant for Simple and RDF entailments. Particularly, this is the case as long as the  RIF ruleset in the combination does not use ##.
Can you confirm this?

If I had a wishlist, I would opt for moving the semantic condition on 

"7. IEXT(IS(rdfs:subClassOf)) is a superset of the set of all pairs (a, b) in Dind x Dind such that Itruth(Isub(a,b))=t;"

to just apply for RIF-RDFS-models "upwards"

Can we still change this?

Axel


Begin forwarded message:

> From: "Ivan Herman" <ivan@w3.org>
> Date: 25 February 2010 09:46:04 GMT
> To: "Polleres, Axel" <axel.polleres@deri.org>
> Cc: "Sandro Hawke" <sandro@w3.org>
> Subject: Re: A technical RIF question
> 
> 
> 
> On 2010-2-25 10:10 , Axel Polleres wrote:
>> 
>> On 25 Feb 2010, at 09:03, Ivan Herman wrote:
>> 
>>> 
>>> On Feb 25, 2010, at 09:56 , Axel Polleres wrote:
>>> 
>>>> Phew, IIRC this has some historic reasons, which I don't really remember.
>>>> 
>>>> Firstly, ## is not the same as rdfs:subclass (e.g. ## is NOT reflexive, IIRC)
>>>> 
>>>> The simple solution is, similar to what I answered to Dan on owl:sameAs:
>>>> 
>>>> just use rdfs:subclass in your rules and don't bother about ## they are not the same thing...
>>>> 
>>> 
>>> Well, o.k. I will try to avoid referring to ## in my tutorial part then...:-(
>>> 
>>>> What worries me a bit more:
>>>> Note that http://www.w3.org/TR/rif-rdf-owl/ restricts RDF-OWL interpretations 
>>>> in such a way that ## implies rdfs:subclass but not the other way around.
>>>> The Embedding of RIF combinations in Section 9.1.3 of
>>>> http://www.w3.org/TR/rif-rdf-owl/ enforces this by a rule... which then makes even the 
>>>> embedding of simple RDF entailment go outside RIF Core... I am not sure whether I like this. :-|
>>>> 
>>> 
>>> Oops. But isn't this a bug? If I talk about an RDF interpretation, than the RDFS vocabulary is immaterial. and subClassOf is in the RDFS vocabulary and _not_ in the RDF vocabulary!
>> 
>> As far as I can see, this is not problematic. We just restrict that when you throw RIF and RDF stuff together,
>> a link is made from ## to rdf:subclasss... that implies that anything which is stated as ## in RIF is exportet to rdfs:subclassOf (but NOT the other way around!) 
>> only in RIF-RDFS-entailment this would have cross-effects (since RDFS interpretations imply reflexivity on rdfs:subclass), but not in RIF-Simple and RIF-RDF
>> 
>> If you agree, I should carry this discussion to the RIF group...
>> 
> 
> Sure
> 
> Ivan
> 
> 
>> HTH,
>> Axel
>> 
>> 
>>> 
>>> I think this is a bug that you should report before this goes to PR:-(
>>> 
>>> Ivan
>>> 
>>> 
>>>> I am not really swapped in on that at the moment, and for more details and clarifications, 
>>>> I'd prefer to get back to the group... 
>>>> 
>>>> Axel
>>>> 
>>>> On 25 Feb 2010, at 08:22, Ivan Herman wrote:
>>>> 
>>>>> (background: I try to update my tutorial slide set...)
>>>>> 
>>>>> Question: what is the background of the fact that '#' is defined for
>>>>> Core and '##' is not?
>>>>> 
>>>>> For many RDF users I would think Core (or maybe strongly safe Core)
>>>>> would be the natural rule set to use in the sense that would cover most
>>>>> of their needs (at least I believe). The fact of having '#' is fine, it
>>>>> is the equivalent of rdf:type. But, for RDFS users, so to say, suddenly
>>>>> there is this gap of '##'; either they have to keep to Core and use
>>>>> explicitly rdfs:subClassOf, or they use '##', thereby getting into BLD...
>>>>> 
>>>>> So: what is the technical reason for this?
>>>>> 
>>>>> Thanks
>>>>> 
>>>>> Ivan
>>>>> -- 
>>>>> 
>>>>> Ivan Herman, W3C Semantic Web Activity Lead
>>>>> Home: http://www.w3.org/People/Ivan/
>>>>> mobile: +31-641044153
>>>>> PGP Key: http://www.ivan-herman.net/pgpkey.html
>>>>> FOAF   : http://www.ivan-herman.net/foaf.rdf
>>>>> vCard  : http://www.ivan-herman.net/HermanIvan.vcf
>>>>> 
>>>> 
>>> 
>>> 
>>> ----
>>> Ivan Herman, W3C Semantic Web Activity Lead
>>> Home: http://www.w3.org/People/Ivan/
>>> mobile: +31-641044153
>>> PGP Key: http://www.ivan-herman.net/pgpkey.html
>>> FOAF: http://www.ivan-herman.net/foaf.rdf
>>> 
>>> 
>>> 
>>> 
>>> 
>> 
> 
> -- 
> 
> Ivan Herman, W3C Semantic Web Activity Lead
> Home: http://www.w3.org/People/Ivan/
> mobile: +31-641044153
> PGP Key: http://www.ivan-herman.net/pgpkey.html
> FOAF   : http://www.ivan-herman.net/foaf.rdf
> vCard  : http://www.ivan-herman.net/HermanIvan.vcf
> 
Received on Thursday, 25 February 2010 10:02:43 GMT

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