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Re: [SWC] Action-830

From: Axel Polleres <axel.polleres@deri.org>
Date: Wed, 03 Jun 2009 13:22:23 +0100
Message-ID: <4A266AFF.7020004@deri.org>
To: Jos de Bruijn <debruijn@inf.unibz.it>
CC: "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>
* I am fine to keep the DL-safeness definitition "as is" for LC.
* I guess the point on the semicolon in the definition of
   multistructures requires Michael Kifer's response.

Axel

Jos de Bruijn wrote:
> 
> Axel Polleres wrote:
>> find my comments inline below. This completes ACION-830
>> http://www.w3.org/2005/rules/wg/track/actions/830
>>
>> Overall, I am fine with most of the changes made wrt.
>> Urgent open points:
>>
>>  - DL-safeness definition.
>>
>>  - Semantic multistructures and dl-multi-structures still look
>> inconsistent.
>>
>> more comments below.
>>
> 
> 
> My responses in-line.
> 
>>>> Section 3.1
>>>> ===========
>>>>
>>>> * Section 3.1.2 "A RIF-RDF combination consists of a RIF document and
>>>> zero or more RDFgraphs"
>>>>
>>>> Why do we allow only 1 RIF dcoument and arbitrary RDF graphs in a
>>>> combination?
>>> Because an RIF document an import any number of RDF graphs.
>>
>>
>> I am not sure whether I understand this reply, but what I
>> asked was why not several RIF documents can be involved, but ...
> 
> Section 5 says how to interpret an RIF document importing a number of
> RDF graphs. There is only one RIF document involved here, and so there
> is no point to define the semantics for combinations involving more than
> one RIF document.
> 
>>>> This means that simple entailment in combination with an empty
>>>> ruleset is not the same as simple entailment in RDF... I think that
>>>> should be pointed out explicitly. It would be also worthwhile to add
>>>> this example,
>>>> i.e. I suggest to add (at the end of Section 3.2.3):
>>>> "Note that simple entailment in combination with an empty ruleset is
>>>> not the same as simple entailment in RDF, since certain entailments
>>>> regarding datatypes are enforced by the RIF-BLD semantics in
>>>> combinations. For instance, given two graphs
>>>>
>>>>  G1= { :s :p "foo" .} and
>>>>  G2= { :s :p "foo"^^xs:string }
>>>>
>>>> as well as an empty RIF document R.
>>>>
>>>>  G1 |=/=_simpleRDF G2
>>>> following [http://link-to-rdf-mt-simple-entailment RDF simple
>>>> entailment] , but
>>>>
>>>>  <R,{G1}> |=_simple <R,{G2}>
>>>> "
>>> There is already an example to this effect in the introduction to
>>> section 3.
>>
>> Then at least a pointer would be worthwhile here, so a short version
>>
>> "Note that simple entailment in combination with an empty ruleset
>>  is not the same as simple entailment in RDF, since certain entailments
>>  regarding datatypes are enforced by the RIF-BLD semantics in
>>  combinations, cf. also Example [pointer-to-example] before."
> 
> done
> 
>>>> Section 4:
>>>> ==========
>>>>
>>>>
>>>> * Section 4.1.1
>>>> "Given a set of OWL 2 DL ontologies O, a variable ?x in a RIF rule Q H
>>>> :- B is DL-safe if it occurs in an atomic formula in B that is not of
>>>> the form s[P -> o] or s[rdf:type -> A], where P or A occurs in one of
>>>> the ontologies in O."
>>>>
>>>> That doesn't seem to be sufficient, take:
>>>>
>>>> ?X [rdf:type -> d ] :- Or ( ?X [rdf:type -> c ] p(?X) )
>>>>
>>>> this is DL-safe according to the definition above but can be expanded
>>>> to two rule one of which wouldn't be DL-safe.
>>>>
>>>> Rather, we need to adopt a safeness notion similar to Core.
>>> You are right. The definition is not sufficient. For now I just defined
>>> it for disjunction-free rules. I hope I will be able to include a proper
>>> safeness condition later on. You can also have a go at it, if you feel
>>> like it.
>> Didn't manage to tackle it either, and will likely not be able this
>> week, sorry.
> 
> Do you think it is critical to have the refined definition in place
> before LC? I think it is OK to refine the definition later, since it is
> already at risk.
> 
>>>> * Section 4.2.2.1
>>>>
>>>>
>>>> *
>>>> Definition (dl-semantic multi-structure):
>>>> "I<sub>1C</sub>, ..., I<sub>1C</sub>"
>>>>
>>>> looks weird, better use 1...n as superscripts as in
>>>> http://www.w3.org/2005/rules/wiki/BLD#def-bld-semantic-multistruct
>>>>
>>>> Again, shouldn't we use \hat{I} rather than I for
>>>> multi-structures as in BLD to be consistent?
>>>>
>>>> *
>>>> same definition:
>>>> Bullet 1 ends with "and ; "
>>>> That looks incomplete, is there anything missing?
>>>>
>>>> *
>>>> "I(&phi;), for any other formula or symbol &phi;, and the truth
>>>> valuation
>>>> function TValI are defined as in BLD semantic structures. "
>>>>
>>>> I am, honestly, getting confused with the definitions of
>>>> multi-structures in BLD vs. SWC.
>>>>
>>>> dl-multistructures consist of {I_1, ..., I_n}
>>>> whereas BLD multistructures are {J,I; I_i1, I_i2, ...}
>>>> so, I am unsure what "defined as in BLD semantic structures."
>>>> means to say.
>>>>
>>>> (BTW: I sent an amendment to my BLD review  per mail in this regard
>>>> as well)
>>> I updated the definition in SWC to reflect the changes in the definition
>>> in BLD. Please have a look.
>>
>>  - semantic multistructures and dl-multi0-structures still look
>> inconsistent:
>>
>> section 4.2.2.1
>>
>>
>> "
>> Formally, a dl-semantic multi-structure  is a set of dl-semantic
>> structures {J,I, Ii1, Ii2, ...}, where "
>>
>> misses th ";" used in BLD... shouldn't this be:
>>
>> "Formally, a dl-semantic multi-structure  is a set of dl-semantic
>> structures {J,I; Ii1, Ii2, ...}, where "
>>
>> ?
> 
> To be honest, I don't understand the ';'. It is a set, and the ',' is
> commonly used to separate the individual elements in a set.
> 
>>
>>  - same here:
>>
>> "Given a dl-semantic multi-structure ={I1, I2, ...}, "
>>
>> should be:
>>
>> "Given a dl-semantic multi-structure ={{J,I; Ii1, Ii2, ...}, "
> 
> It is a set of structures, so it does not really matter which symbols I
> use for the individual elements.
> 
> 
> Cheers, Jos
> 


-- 
Dr. Axel Polleres
Digital Enterprise Research Institute, National University of Ireland, 
Galway
email: axel.polleres@deri.org  url: http://www.polleres.net/
Received on Wednesday, 3 June 2009 12:23:01 GMT

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