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Re: SKOS Comment: skos:broader as subproperty of broaderTransitive seems backwards

From: Antoine Isaac <aisaac@few.vu.nl>
Date: Mon, 01 Dec 2008 14:53:54 +0100
Message-ID: <4933EC72.8040307@few.vu.nl>
To: "Booth, David (HP Software - Boston)" <dbooth@hp.com>
CC: "public-swd-wg@w3.org" <public-swd-wg@w3.org>

Hi David,

There is a small note in the SKOS Primer about this issue [1]. Your feedback on whether this is appropriate would be warmly welcome!

Best regards,

Antoine Isaac

[1] http://www.w3.org/TR/2008/WD-skos-primer-20080829/#sechierarchy


> Hi Sean,
> 
> Good point and explanation!  So skos:broader does have *some* transitivity, but it is only transitive to the extent that a skos:broader relations is a skos:broaderTransitive relation -- the semantics of skos:broader that are distinct from the semantics of skos:broaderTranstive are not transitive.
> 
> It might be worth adding or linking to your explanation in a future draft, since others may puzzle over this also.
> 
> Thanks
> 
> David Booth, Ph.D.
> HP Software
> +1 617 629 8881 office  |  dbooth@hp.com
> http://www.hp.com/go/software
> 
> Statements made herein represent the views of the author and do not necessarily represent the official views of HP unless explicitly so stated.
> 
> 
>> -----Original Message-----
>> From: Sean Bechhofer [mailto:sean.bechhofer@manchester.ac.uk]
>> Sent: Monday, December 01, 2008 5:18 AM
>> To: Booth, David (HP Software - Boston)
>> Cc: public-swd-wg@w3.org
>> Subject: Re: SKOS Comment: skos:broader as subproperty of
>> broaderTransitive seems backwards
>>
>>
>> On 1 Dec 2008, at 07:50, Booth, David (HP Software - Boston) wrote:
>>
>>> In
>>> http://www.w3.org/TR/2008/WD-skos-reference-20080829/#L2413
>>> it says that "skos:broader is not a transitive property", but
>>> "skos:broader is a sub-property of skos:broaderTransitive, which is
>>> a transitive property".  Isn't this backwards?
>>>
>>> By the entailment rules for rdfs:subPropertyOf
>>> http://www.w3.org/TR/rdf-mt/#rulerdfs7
>>> if:
>>>         skos:broader rdfs:subPropertyOf skos:broaderTransitive .
>>>         uuu skos:broader yyy .
>>>
>>> then necessarily:
>>>
>>>         uuu skos:broaderTransitive yyy .
>> David
>>
>> A subproperty of a transitive property is not necessarily transitive.
>> As you rightly point out, if I have
>>
>> xxx skos:broader yyy
>>
>> then I can infer
>>
>> xxx skos:broaderTransitive yyy
>>
>> However, this doesn't mean skos:broader is transitive. If a relation
>> R is transitive, it means that from xRY and yRz, we can infer xRz. So
>> the situation with broader is as follows.
>>
>> If I have
>>
>> xxx skos:broader yyy
>> yyy skos:broader zzz
>>
>> then I can infer (through subproperties) that
>>
>> xxx skos:broaderTransitive yyy
>> yyy skos:broaderTransitive zzz
>>
>> Now, due to the transitivity of broaderTransitive, I can infer
>>
>> xxx skos:broaderTransitive zzz
>>
>> This *doesn't* mean that xxx skos:broader zzz, so I don't
>> (necessarily) have transitivity of skos:broader.
>>
>> The WG spent some time discussing this. We believe that there are
>> situations where we do not necessarily want skos:broader to be
>> transitive, but the pattern we have used allows us to /query/ across
>> something which includes the transitive closure of skos:broader,
>> without us having to assert that skos:broader is itself transitive.
>> We believe that this is the desirable situation.
>>
>> Hope that helps.
>>
>>         Sean
>>
>> --
>> Sean Bechhofer
>> School of Computer Science
>> University of Manchester
>> sean.bechhofer@manchester.ac.uk
>> http://www.cs.manchester.ac.uk/people/bechhofer
>>
>>
>>
>>
> 
> 
Received on Monday, 1 December 2008 13:54:32 UTC

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