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Re: summary of reification?

From: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
Date: Thu, 07 Feb 2002 10:08:06 +0000
Message-Id: <5.1.0.14.2.20020207100306.039445a0@joy.songbird.com>
To: Pat Hayes <phayes@ai.uwf.edu>
Cc: w3c-rdfcore-wg@w3.org
At 05:25 PM 2/6/02 -0600, Pat Hayes wrote:
>>At 12:25 PM 2/6/02 -0600, Pat Hayes wrote:
>>>>I see two ways of how the semantics of reification could be attacked:
>>>>
>>>>1. Explain the semantics using bNode + 4-triple constructs. Applications
>>>>are free to use a compact representation. If statements are used as
>>>>first-class objects, they can be treated just as some kind of bNodes.
>>>>The API-level identity of such bNodes is functionally determined by
>>>>their (s,p,o)-description. Alternatively, the applications can generate
>>>>exactly one such bNode for each (s,p,o) etc. Same trick could be applied
>>>>for  dealing with functionally determined bNodes in the model theory.
>>>
>>>No trick is needed. The ordinary MT already would treat the 4-triples in 
>>>this way already; reification is semantically transparent, on this view. 
>>>Which is another way of saying that we are trashing it. After all, 
>>>there's no way to stop anyone writing those 4-triples if they want to, 
>>>right? Trashing it doesn't make it illegal, it just says that we aren't 
>>>saying anything particular about what it means: its not a language 
>>>feature, its just a way you might want to write some RDF. Go ahead if 
>>>y'all feel like it.
>>
>>I want to pick up on two points here:
>>
>>(1) there is provision (in RDFM&S) for a reified statement to be 
>>identified (e.g. by rdf:ID='xxx' on the corresponding property element), 
>>so simply saying reified statements are treated as bNodes seems to miss 
>>something.
>
>Ah, that is exactly what I wanted to focus on. WHAT DOES THAT MEAN ?? To 
>'identify' a reified statement, that is. Is the identifying ID a URI? If 
>so, then why doesnt the 4-triple use that URI instead of a bnode? If not, 
>what can 'identify' possibly mean in RDF?

Well, by my reading of current M&S, I think is does;  i.e.

    <rdf:Description rdf:about='ex:subj'>
       <ex:prop rdf:id='ex:reif' rdf:resource='ex:obj'/>
    </rdf:Description>

yields:

    <ex:reif> <rdf:type> <rdf:Statement> .
    <ex:reif> <rdf:subject> <ex:subj> .
    <ex:reif> <rdf:predicate> <ex:prop> .
    <ex:reif> <rdf:object> <ex:obj> .

which was my point:  I didn't think the statement resource was necessarily 
a bnode.

(Of course, this entails the bnode case, right?)

#g
--

>>(2) accepting almost all of the above that the reification properties are 
>>mostly like any other RDF properties, we need to express a view on this 
>>entailment:
>>
>>     <ex:subj> <ex:prop> <ex:obj> .
>>entails
>>     _:r <rdf:type> <rdf:Statement> .
>>     _:r <rdf:subject> <ex:subj> .
>>     _:r <rdf:predicate> <ex:prop> .
>>     _:r <rdf:object> <ex:obj> .
>>?
>>
>>What you say above suggests no such entailment.
>
>Right.
>
>Pat
>
>--
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------------------------------------------------------------
Graham Klyne                    MIMEsweeper Group
Strategic Research              <http://www.mimesweeper.com>
<Graham.Klyne@MIMEsweeper.com>
Received on Thursday, 7 February 2002 05:46:35 EST

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