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

From: Jos de Bruijn <jos.debruijn@gmail.com>
Date: Thu, 25 Feb 2010 11:19:18 +0100
Message-ID: <4B864EA6.3020305@gmail.com>
To: Axel Polleres <axel.polleres@deri.org>
CC: RIF <public-rif-wg@w3.org>
Why ## is not in Core: different people had different reasons for not
wanting ## in Core. In the end there were fewer people who wanted it
than who did not, so it did not get in.

Concerning the bug: there is indeed a claim at the start of the appendix
that the embedding is in Core, while it is not.
I would suggest to include a caveat saying that when operating in Core,
the one rule concerning ## should be disregarded.

I would find it kind of awkward to have ontology modeling vocabulary (#
and ##) in RIF-RDF combinations without tying it in with the RDF
ontology modeling vocabulary, even when using only simple entailment. I
think this would be awkward for people, especially when querying the RDF
entailments. Therefore, I would not favor your proposed solution.


Cheers, Jos

On 2010-02-25 11:02, Axel Polleres wrote:
> 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
>> 
> 
> 

-- 
Jos de Bruijn
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Received on Thursday, 25 February 2010 10:19:09 GMT

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