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Re: PROV-ISSUE-526: Data Model Section 5.5.2 [prov-dm]

From: James Cheney <jcheney@inf.ed.ac.uk>
Date: Fri, 28 Sep 2012 11:25:13 +0100
Cc: Paolo Missier <Paolo.Missier@ncl.ac.uk>, public-prov-wg@w3.org
Message-Id: <939A6435-DE8F-4D29-A4DF-341E96196E97@inf.ed.ac.uk>
To: Graham Klyne <graham.klyne@zoo.ox.ac.uk>
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On Sep 27, 2012, at 10:20 PM, Graham Klyne wrote:

> On 27/09/2012 19:58, Paolo Missier wrote:
>> sorry it is consistent, I ignored inf. 20 (specialization implies alternate) and
>> just assumed that two entities that belong to the same equivalence class should
>> not be in a specialization hierarchy.
>> But then I just realized I don't quite understand the point of Inf. 20: Why has
>> it been introduced?
>> 
>> you now have that specializations create equivalence classes, in particular
>> 
>> a specializationOf b
>> a specializationOf c
>> 
>> implies a alternateOf b and a alternateOf c
>> and therefore
>> b alternateOf c
>> 
>> which is a bit odd. For an OWL-inclined reader, specialization has a SubClassOf
>> flavour, so this would be
>> 
>> Mother specializationOf Woman
>> Mother specializationOf Parent
>> 
>> therefore Woman and Parent are "alternates" -- this seems to make the
>> interpretation of "alternateOf" even more mysterious. Or is it just me
> 
> The above works for me.
> 
> If you adopt a class-oriented (OWL?) perspective, the alternateOf here would seem a bit odd.  But I'd see it applied to a single person, say Alice, a mother, when considering:
> 
>  Alice as a woman
> and
>  Alice as a parent
> 
> To me, these seem quite reasonable as alternativeOf views of Alice.
> 

Hi all,

This seems to be revisiting ISSUE-29, whose resolution (I believe) agreed the definitions and inferences relating alternate and specialization to each other.

Inference 20 says that specialization is a kind of alternate.  This seems (to me) to follow from their English definitions [1]

> An entity that is a specialization ◊ of another shares all aspects of the latter, and additionally presents more specific aspects of the same thing as the latter. In particular, the lifetime of the entity being specialized contains that of any specialization.
...
> 
> Two alternate ◊ entities present aspects of the same thing. These aspects may be the same or different, and the alternate entities may or may not overlap in time. 

So I think this issue can be resolved by adding explanation of the intended use of specialization (not as "subclass", but as "entity presenting more specific aspects of thing than another alternate entity") and alternate (as "different aspects of the same thing").  Perhaps additional remarks are needed to motivate the inferences in the constraints document too.

I believe a conclusion of the resolution of ISSUE-29 was that other "part of" or "is-a" relationships were not to be conflated with specialization - specifically, specialization does not necessarily align with containment in a collection or membership between an instance and a class.  If we blur these distinctions, then we indeed get strange things (riffing on Paolo's example):

Alice isa parent => Alice specializationOf parent => Alice alternateOf parent
Bob isa parent =>  Bob specializationOf parent => Bob alternateOf parent

....therefore, by symmetry/transitivity....

Alice alternateOf Bob.

which is absurd.  So we should not (and currently do not) identify specialization with isa or subtype relationships (which are of course handled in RDF/Owl already, and we should not reinvent).

--James

[1] http://www.w3.org/TR/prov-dm/#component5

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Received on Friday, 28 September 2012 10:26:07 GMT

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