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

From: Luc Moreau <L.Moreau@ecs.soton.ac.uk>
Date: Thu, 28 Jul 2011 15:14:43 +0100
Message-ID: <EMEW3|7434b6ed53f368e4723d8bf7edb7e4cbn6RFEk08L.Moreau|ecs.soton.ac.uk|4E316ED3.2030909@ecs.soton.ac.uk>
To: public-prov-wg@w3.org
Yes, Stephen, that seems to be the consequence of this definition.
Is it the property we want?

Luc

On 07/28/2011 03:02 PM, Cresswell, Stephen wrote:
>
> Paolo,
>
> The "holds over the temporal intersection" clause is already there in 
> the definition of IVPof.  I am questioning the transitivity of the 
> relation even with this clause.  I think that inference of IVPof using 
> transitivity from two IVPof assertions is only valid if all three bobs 
> involved have mutually overlapping intervals (i.e. X must overlap Z in 
> my example), and it is this condition which is not captured.
>
> Stephen Cresswell
>
> Tel:  +44 (0) 01603 69 6926
>
> Web: www.tso.co.uk <http://www.tso.co.uk/>
>
> ------------------------------------------------------------------------
>
> *From:* Paolo Missier [mailto:Paolo.Missier@ncl.ac.uk]
> *Sent:* 28 July 2011 14:29
> *To:* Cresswell, Stephen
> *Cc:* public-prov-wg@w3.org
> *Subject:* Re: PROV-ISSUE-45: isDerivedFrom and IVPof are transitive. 
> [Conceptual Model]
>
> 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> 
> [mailto:public-prov-wg-request@w3.org] *On Behalf Of *Paolo Missier
> *Sent:* 25 July 2011 12:30
> *To:* public-prov-wg@w3.org <mailto: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  <mailto:Paolo.Missier@newcastle.ac.uk>,pmissier@acm.org  <mailto:pmissier@acm.org>  
> School of Computing Science,Newcastle University,UK
> http://www.cs.ncl.ac.uk/people/Paolo.Missier
>
>
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-- 
Professor Luc Moreau
Electronics and Computer Science   tel:   +44 23 8059 4487
University of Southampton          fax:   +44 23 8059 2865
Southampton SO17 1BJ               email: l.moreau@ecs.soton.ac.uk
United Kingdom                     http://www.ecs.soton.ac.uk/~lavm
Received on Thursday, 28 July 2011 14:15:34 GMT

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