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

From: Paolo Missier <Paolo.Missier@ncl.ac.uk>
Date: Thu, 28 Jul 2011 14:29:23 +0100
Message-ID: <4E316433.9020402@ncl.ac.uk>
To: "Cresswell, Stephen" <stephen.cresswell@tso.co.uk>
CC: "public-prov-wg@w3.org" <public-prov-wg@w3.org>
Stephen,

your observation is correct, of course, and it does make the IVP-of relation look not well-behaved, but that's because the temporal 
interval that defines Bobs validity explicitly, has remained  "hidden" in the def. of IVP-of relation, while it should have been 
made explicit there, as well.
  So if you add your sentence "B IPVof A is defined to only hold over the temporal intersection of A and B" to the def. of IVP-of 
(as we should have done as it makes no sense to establish a relation between two Bobs, one of which is out of scope), then over this 
restricted interval the relation /is/ transitive, right?
What I mean is that the problem is not that IVP-of is not transitive, but that in the def. we omitted to qualify the scope within 
which the relation itself holds.

Regarding better-behaved relations, personally (and bear in mind this is not /my/ def.) I rather like the general case in which
- the set of attributes overlap (with no strict set containment requirement)
- the temporal scopes overlap (with no strict interval containment requirement)
as these conditions lead, within a possibly restricted scope, to an equivalence relation.  That said, whether this is still 
practically useful is a separate issue...

-Paolo

On 7/28/11 1:13 PM, Cresswell, Stephen wrote:
>
> Paolo,
>
> 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]
>
> Khalid
>
> 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.
>
> -Paolo
>
>
>   
>   
> PROV-ISSUE-45: isDerivedFrom and IVPof are transitive. [Conceptual Model]
>   
> http://www.w3.org/2011/prov/track/issues/45
>   
> 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.
>   
> khalid
>
>
>
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-- 
-----------  ~oo~  --------------
Paolo Missier - Paolo.Missier@newcastle.ac.uk, pmissier@acm.org
School of Computing Science, Newcastle University,  UK
http://www.cs.ncl.ac.uk/people/Paolo.Missier
Received on Thursday, 28 July 2011 13:30:04 GMT

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