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RE: PROV-ISSUE-45: isDerivedFrom and IVPof are transitive. [Conceptual Model]

From: Cresswell, Stephen <stephen.cresswell@tso.co.uk>
Date: Thu, 28 Jul 2011 13:13:22 +0100
Message-ID: <F22D0BFCDD4DDC44B92C4E24D751CB9362CF6C@W3EXC017023.theso.co.uk>
To: "Paolo Missier" <Paolo.Missier@ncl.ac.uk>, <public-prov-wg@w3.org>



I don't see how IVPof can be usefully considered transitive in its
current definition, as I think it would be possible for some
transitively-derived IVPof relations to be valid only over empty time
intervals.  This is because B IPVof A is defined to only hold over the
temporal intersection of A and B, but the relation of having non-empty
temporal intersection is itself not transitive.  


For example, we can have three time intervals X, Y, Z such that X
overlaps Y, Y overlaps Z, but X is disjoint from Z.

Then if we have bobs Bx, By, Bz which hold over the respective time
intervals, and we asserted 

Bx IVPof By

By IVPof Bz

... then transitivity would allow us to derive 

Bx IVPof Bz

... but that is dubious because it would hold only over the temporal
intersection of X and Z, which is empty.


I was hoping that the definition of B IVPof A would turn out to require
that the time interval of B was contained in the time interval of A.  I
think that would be a simpler and better-behaved relation, which should
be glorified with a name, even it's not "IVPof".


Stephen Cresswell

Tel:  +44 (0) 01603 69 6926

Web:  www.tso.co.uk <http://www.tso.co.uk/> 



From: public-prov-wg-request@w3.org
[mailto:public-prov-wg-request@w3.org] On Behalf Of Paolo Missier
Sent: 25 July 2011 12:30
To: public-prov-wg@w3.org
Subject: Re: PROV-ISSUE-45: isDerivedFrom and IVPof are transitive.
[Conceptual Model]



I don't think we have ever agreed on that, but I should really check the
voting history. The latest definition of IVP-of (or complement-of) is
sufficiently precise (i.e., algorithmic) that transitivity follows, but
derivation is purely asserted and as such there is no ground to say that
it is transitive -- unless we say axiomatically that it should be.


PROV-ISSUE-45: isDerivedFrom and IVPof are transitive. [Conceptual
Raised by: Khalid Belhajjame
On product: Conceptual Model
If we agree that "isDerivedFrom" and "IVPof" are transitive, then I
would suggest that this should be specified in the model working draft.

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Received on Thursday, 28 July 2011 12:13:53 UTC

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