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

From: Luc Moreau <l.moreau@ecs.soton.ac.uk>
Date: Wed, 08 Aug 2012 09:59:25 +0100
Message-ID: <EMEW3|897e274decf83b7029d212689bf66d38o779xU08l.moreau|ecs.soton.ac.uk|50222A6D.4070007@ecs.soton.ac.uk>
To: public-prov-wg@w3.org
Hi Stian,

The constraints are about event ordering and not time ordering. The 
specification is silent about how
time information should be ordered.  A given application, with knowledge 
that a same clock is used for
all time information, could check further constraints. E.g. time 
ordering is compatible with event ordering.

However, we now have a framework to provide further constraints for 
extensions to PROV.
If someone was defining  ex:hadSubactivity(a,a1),
we could imagine
wasStarted(start; a, -,-,-)
wasStarted(start1; a1, -,-,-)
a strictly precedes a1

and symmetrically for end.


On 08/08/12 09:36, Stian Soiland-Reyes wrote:
> On Mon, Aug 6, 2012 at 4:54 PM, James Cheney <jcheney@inf.ed.ac.uk> wrote:
>> In internal discussion, we basically decided to make all of the constraints non-strict except the two involving derivation.  (The entity-generation-use one slipped through accidentally.)
>> I see no reason to insist on the generation-use in derivation to be strictly-precedes, so I propose to weaken it to "precedes" unless anyone wants to make a case for it.
> Sounds good. I just have one note (which should not affect this issue
> unless you object) then about checking for time order constraints, as
> the specification asks us to check for any loops with strictly
> precedes. So if there are no derivations, you can't detect time order
> violations, although all such such loops would then collapse to be
> single instants. (Which timestamps might then informally suggest is
> not the case).
> Would there be any other way to detect the time order violations if
> there are no derivations?
> I suspect not, as there is no way in PROV alone to specifically state
> time relations or durations - but there might be application specific
> knowledge, for instance that ex:photocopying takes usually a second,
> and ex:faxing takes usually at least 30 seconds, and thus a received
> fax could not be photocopied at the same time as the fax was sent.

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 Wednesday, 8 August 2012 08:59:59 UTC

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