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Re: firts and rdf:rest as functional property

From: Bijan Parsia <bparsia@cs.man.ac.uk>
Date: Fri, 20 Mar 2009 13:52:14 +0000
Message-Id: <C87395D2-D3B6-4707-8251-750BA1C87478@cs.man.ac.uk>
Cc: Michael Schneider <schneid@fzi.de>, Semantic Web <semantic-web@w3.org>
To: Reto Bachmann-Gmür <reto.bachmann@trialox.org>
Hi Reto,

On 20 Mar 2009, at 13:25, Reto Bachmann-Gmür wrote:

> Hi Michael
> Sorry for the late replay.
> Michael Schneider said the following on 02/18/2009 08:49 PM:
>> ...
>> But why does anybody want semantic constraints for lists at all? One
>> certainly does not want to reason about duplicate rdf:first  
>> occurrences,
>> right? What one probably rather wants is to make sure that lists are
>> structurally ok. And, I guess, for all realistic scenarios, a  
>> syntax checker
>> will simply do the job.
> The main reason I see that if rdf:rest is a functional property a  
> graph
> can be decomposed without loss into much smaller components.

I think you misunderstood Michael's point. Basically, you can enforce  
"sensible listness" either *syntactically* or *semantically*. In  
point of fact, first order logic is too weak (in any case) to rule  
out models with non-standard lists semantically (i.e., by  
axiomization, at least in the general case).

Furthermore, it seems reasonable to think that in the common use of  
rdf:list, the concern is with *explicit* list structures, i.e., to  
check that all and only the part of "nice lists" are explicit in the  
data. This suggests a syntactic, rather than a semantic, approach. To  
put it another way, what's needed is integrity constraint like  
checks, not cardinality inferences.

> If rdf:rest
> and rdf:first are not functional a list could typically not be be
> splitted into different rdf molecules[1]. Splitting graphs into small
> components is essential for applications like diff, sync[2] and
> versioning[3].

If you are doing to decompose *semantically*, then functionality will  
be too weak to do the job anyway.

Received on Friday, 20 March 2009 13:48:33 UTC

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