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

From: Provenance Working Group Issue Tracker <sysbot+tracker@w3.org>
Date: Mon, 06 Aug 2012 15:34:55 +0000
Message-Id: <E1SyPKZ-0002QM-Sp@tibor.w3.org>
To: public-prov-wg@w3.org
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. "
Received on Monday, 6 August 2012 15:34:57 UTC

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