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Re: PROV-ISSUE-157 (TLebo): wasInformedBy's non-transitivity

From: Luc Moreau <L.Moreau@ecs.soton.ac.uk>
Date: Mon, 21 Nov 2011 16:12:44 +0000
Message-ID: <EMEW3|59f2db58c32ba21733fcf3760a867213nAKGCl08L.Moreau|ecs.soton.ac.uk|4ECA787C.8080008@ecs.soton.ac.uk>
To: public-prov-wg@w3.org
Hi Tim,
Responses interleaved.

On 11/21/2011 03:26 PM, Provenance Working Group Issue Tracker wrote:
> PROV-ISSUE-157 (TLebo): wasInformedBy's non-transitivity
>
> http://www.w3.org/2011/prov/track/issues/157
>
> Raised by: Timothy Lebo
> On product:
>
> The argument that wasInformedBy is not transitive is not clear and convincing.
>
> 1) Does the diagram correctly illustrate the assertions wasInformedBy(a2,a1) and wasInformedBy(a3,a2), and wasInformedBy(a3,a1)? There seems to be a lot of additional unstated assumptions that are embodied by the diagram beyond these three DM assertions.
>    

Hmm .. which?

> 2) It appears that the counterexample is using a "degenerate" situation, when the argument for non-transitivity can ALSO be made for activities following a more natural time flow (e.g., even when e2 is used AFTER e1 is generated). In this situation, we do not _know_ that the information in e2 is related to the information in e1 _in any way_.
>    

I don't think we have made a transivity claim in the example you suggest 
(e2 used after e1).

The point, which I would like to adopt across the whole document, is 
that I would like to explain non-transitivity property for
all relevant relations.

> 3) There is a "Note: This relation to be simplified using wasStartedBy/wasEndedBy.". Could someone point me to the expected changes here?
>
>
>    
Sorry, it was a note to me, it is the following relation 
wasScheduledAfter that needs simplifying.
Luc

> Thanks,
> Tim
>
>
> Reference:
>
>
> http://dvcs.w3.org/hg/prov/raw-file/default/model/ProvenanceModel.html#record-OrderingOfActivities :
>
> """
> The relationship wasInformedBy is not transitive. Indeed, consider the records wasInformedBy(a2,a1) and wasInformedBy(a3,a2), the record wasInformedBy(a3,a1), may not necessarily hold, as illustrated by the following event line.
>
>              ------  a1
>               |
>               e1
>               |
>         -------  a2
>          |
>          e2
>          |
>       -----  a3
>
> The end in activity record identified by a3 precedes the start in activity record identified by a1, while interval for activity record a2 overlaps with each interval for a1 and a3, allowing information to flow (e1 and e2, respectively).
> """
>
>
>
>    

-- 
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 Monday, 21 November 2011 16:13:14 UTC

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