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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 14:36:40 +0000
Message-Id: <6567960D-AA3C-4C1F-BE38-0029E61A2407@cs.man.ac.uk>
Cc: Michael Schneider <schneid@fzi.de>, Semantic Web <semantic-web@w3.org>
To: Reto Bachmann-Gmür <reto.bachmann@trialox.org>
On 20 Mar 2009, at 14:22, Reto Bachmann-Gmür wrote:

> Bijan Parsia said the following on 03/20/2009 03:14 PM:
>> On 20 Mar 2009, at 14:02, Reto Bachmann-Gmür wrote:
>>> Hi Bijan
>>>> ...
>>>>> 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.
>>> Not sure if I understand you, if a do decomposition of a graph  
>>> into RDF
>>> molecules[1] (as this is done in the Graph Versioning System GVS  
>>> [2]) if
>>> the base ontology contains the fact that rdf:rest and rdf:firts are
>>> owl:functionalProperty a list will typically (i.e. if some of the
>>> objects of the rdf:first statements are grounded or if the first
>>> rdf:List resource is grounded) be split into many small  
>>> components while
>>> otherwise it is (assuming the rdf:List resources are anonymous) all
>>> contained in one molecule. Isn't the decomposition into a semantical
>>> decomposition?
>> Sorry, don't have time to peek at that at the moment.
>> By semantic decomposition, I mean that there will be certain
>> properties preserved in the decomposition. See the slides for:
>>     http://owl.cs.manchester.ac.uk/2008/iswc-modtut/
> Indeed it seems we are not talking about the same, I'm talking about
> lossless decomposition of graphs, i.e. a decomposition that has the
> property that the union of the components expresses the same  
> meaning as
> the original graph.

That is my meaning.

>> Functionality isn't necessarily the problem, but I presume you want
>> first to be min1 as well (for a well formed list...having holes is as
>> bad as having tentacles).
> That's not an issue for decomposition.

Why not?

>> Functionality might have the surprising effect of entailing that two
>> things are the same. Which might not be how you want to "repair" the
>> tentacled list.
> It's not about repairing list, but its exactly about having means of
> knowing that "two" things are the same

Yes, for this you should be looking at conservativity. Lists are just  
more abox statements. You don't need them to be nice to decompose  
them properly.

>> So, it's not clear to me that this is the right tool for the job.
>> Perhaps I'm wrong about what job you're trying to do?
> If you have some time at some point I invite you check out the Graph
> Versioning System and see the effect of not asserting that the list
> properties are functional of the size of the components containing  
> large
> lists.

But this is irrelevant to the semantic correctness of the decomposition.

>> rdf:Lists were not introduced for modeling, but for encoding the
>> syntax of OWL (taken from DAML+OIL). They have been pressed into
>> service for modeling, but the built-in semantics (IMHO) as well as
>> other aspects of them aren't really suited for modeling. But we model
>> with what's at hand.
> Don't see why we should have other list structure to describe lists
> outside the owl ontology specification.

I'm just pointing out that rdf:list is not a real list nor is it  
properly designed for representing lists. So it'll be hacky.

Received on Friday, 20 March 2009 14:32:59 UTC

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