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Re: [SWC] Action-830

From: Jos de Bruijn <debruijn@inf.unibz.it>
Date: Wed, 03 Jun 2009 13:15:17 +0200
Message-ID: <4A265B45.9000808@inf.unibz.it>
To: Axel Polleres <axel.polleres@deri.org>
CC: "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>


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



Received on Wednesday, 3 June 2009 11:12:56 GMT

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