Re: To embed or combine

Michael Kifer wrote:
>>> The most important argument is that the embedding stands on its own feet,
>>> while the combined semantics is of limited use, since we need the embedding
>>> anyway.
>> We don't necessarily /need/ the embedding if we define a model-theoretic
>> combination [*], it is just nice to have as an appendix, to show how
>> reasoning can be done with the combination.  Just like, as you suggested
>> in an earlier e-mail, we could use the model-theoretic combination in an
>> appendix as a justification for choosing a particular embedding in case
>> we go for the embedding.
> 
> Publish the semantics without the embedding, and see what the reaction will be.
> I suspect that it will be: Huh? What do I do with this?

Yes, probably.  And publish the embedding without any justification and
the reaction will be:  Why this embedding?

> 
> The point is that the embedding is trivial and easy to explain. 

It is certainly not trivial.
Whether it is easier to explain is a matter of point of view, and also
depends on to whom you are explaining it.

>>> Regarding (2) my argument was not what you wrote, but that Jos' document
>>> essentially specifies a full-blown combined language. The embedding alone
>>> is sufficient in my view. It allows people to use rules and RDF together,
>>> but it does not define a normative combined language.  By defining an
>>> embedding, we already achieve all the goals with respect to RDF, which were
>>> listed in the charter.
>> Whether we define the semantics of the combination based on a model
>> theory or based on an embedding in RIF, in both cases we define a
>> combined language, which is normative.
> 
> You can put it this way, but then any embedding of any rule language into
> RIF can be viewed as a combined RIF-LanguageX language. Normally people
> will not view it this way.

The point is that RDF is not a rule language, but a data language. So,
people will want to exchange rules referring to RDF data sets.  The
agents receiving the rules and the data will have to *combine* them in
some way in order to process them.

When exchanging any rule language using RIF, nothing will have to be
combined, so in this case (as you said) people will indeed not view it
as a combined language.


Best, Jos


> 
> 
> 
> 	--michael  
> 
> 
>> Best, Jos
>>
>>>
>>> 	--michael  
>>>
>>>> <chair>
>>>> The status of the discussion regarding Jos' RDF compatibility section appears to 
>>>> be mired in whether the normative semantics of RDF in RIF should be specified in 
>>>> the model theory through a "combination" of RIF and RDF semantics, or through an 
>>>> "embedding" of RDF semantics in RIF (as rules).  The two approaches have been 
>>>> shown by Jos to be equivalent.
>>>>
>>>> At the moment I have not seen any technical arguments supporting one approach or 
>>>> the other.  Michael prefers the "embedding" on the basis that:
>>>>
>>>> (1) the "combination" is more complicated than the "embedding" and thus more 
>>>> difficult to understand.
>>>>
>>>> (2) it is not our job viz. our charter to specify a model theoretic approach to 
>>>> the RDF/RIF combination
>>>>
>>>> Jos seems to prefer the "combination" and argues re: (1) that:
>>>>
>>>> (3) it is no more difficult to understand the "combination" than the RIF model 
>>>> theory.
>>>>
>>>> As chair, my own read of the charter does not provide any particular help on 
>>>> (2), I'm not quite sure what Michael is referring to there.  It is certainly our 
>>>> job to specify how RIF and RDF should be used together, and as chair I interpret 
>>>> this as meaning we should have a normative standard for that.
>>>>
>>>> Thus, as suggested by Michael, it seems to me we are at a difference in 
>>>> preference only, and I see no alternative other than to call a vote.  It seems 
>>>> to me the vote is about which approaches to make *normative*:
>>>>
>>>> 1) The model-theoretic "combination" of RIF and RDF is normative
>>>> 2) The "embedding" of RDF semantics as RIF rules is normative
>>>> 3) Both the "combination" and "embedding" are normative (What would that mean?)
>>>> </chair>
>>>>
>>>> -Chris
>>>>
>>>>
>>>> -- 
>>>> Dr. Christopher A. Welty                    IBM Watson Research Center
>>>> +1.914.784.7055                             19 Skyline Dr.
>>>> cawelty@gmail.com                           Hawthorne, NY 10532
>>>> http://www.research.ibm.com/people/w/welty
> 

-- 
Jos de Bruijn            debruijn@inf.unibz.it
+390471016224         http://www.debruijn.net/
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