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Re: PROV-ISSUE-470 (wasDerFrom-strictly): wasDerivedFrom requires use strictly before generation - why? [prov-dm-constraints]

From: James Cheney <jcheney@inf.ed.ac.uk>
Date: Mon, 6 Aug 2012 16:54:51 +0100
Message-Id: <CAB6E85E-7BF3-47F8-80FB-485E5DF54FCC@inf.ed.ac.uk>
To: Provenance Working Group <public-prov-wg@w3.org>
In internal discussion, we basically decided to make all of the constraints non-strict except the two involving derivation.  (The entity-generation-use one slipped through accidentally.)

I see no reason to insist on the generation-use in derivation to be strictly-precedes, so I propose to weaken it to "precedes" unless anyone wants to make a case for it.

--James

On Aug 6, 2012, at 4:34 PM, Provenance Working Group Issue Tracker wrote:

> PROV-ISSUE-470 (wasDerFrom-strictly): wasDerivedFrom requires use strictly before generation - why? [prov-dm-constraints]
> 
> http://www.w3.org/2011/prov/track/issues/470
> 
> Raised by: Stian Soiland-Reyes
> On product: prov-dm-constraints
> 
> wasDerivedFrom(e2,e1,use,gen) requires use strictly before generation - why?
> 
> I think it makes sense for wasDerivedFrom(e2,e1) to require generation of e1 to strictly precede e2, it follows from DM definition. However I don't get why the activity's use of e1 must strictly precede gen - what is the activity required to do in this period inbetween?
> 
> 
>> From Stian's review http://lists.w3.org/Archives/Public/public-prov-wg/2012Aug/0021.html
> 
> 
> 
> 
>> First, we consider derivations, where the activity and usage are known.
> -->
> First, we consider derivations where the activity and usage are known. In
> 
>> the usage of e1 has to precede the generation of e2
> 
> --> ".. has to strictly precede ..."
> 
> 
> This needs a similar explanation for why this needs to be strictly
> preceded. Use and generation do not require this on their own.  I am
> not sure what the reasoning here, perhaps it has to do with the
> semantics of being 'derived'?
> 
>> http://www.w3.org/TR/prov-dm/#dfn-wasderivedfrom
>> A derivation ◊ is a transformation of an entity into another, an update of an entity resulting in a new one, or the construction of a new entity based on a pre-existing entity.
> 
> This definition places a strict time order, it forces an 'older' and
> 'newer' entity. However I find it strange to apply this to the *usage*
> event, and would rather keep only the following constraint:
> 
>> Constraint 42 (derivation-generation-generation-ordering)
>> IF wasDerivedFrom(_d;e2,e1,attrs) and wasGeneratedBy(gen1;e1,_a1,_t1,_attrs1) and wasGeneratedBy(gen2;e2,_a2,_t2,_attrs2) THEN gen1 strictly precedes gen2.
> 
> Thus use1 precedes gen2  (but not strictly), constraint 41 can be
> reformulated as a corollary with constraint 42+39.  I don't see a good
> reasoning for that to be strictly.
> 
> 
> A  suggested Remark for constraint 42:
> "This constraint, similar to constraint 38, requires the derived
> entity to be generated strictly following the generation of the
> original entity. This follows from the <a>PROV-DM description of
> derivation</a>,  A derivation is a transformation of an entity into
> another, an update of an entity resulting in a new one, or the
> construction of a new entity based on a pre-existing entity</em>, thus
> the derived entity must be newer than the original entity. "
> 
> 
> 
> 
> 


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Received on Monday, 6 August 2012 15:55:14 UTC

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