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Re: PROV-ISSUE-467 (activity-start-req-trigger): Do activity start/end always require trigger? [prov-dm-constraints]

From: James Cheney <jcheney@inf.ed.ac.uk>
Date: Thu, 9 Aug 2012 10:59:00 +0100
Cc: Luc Moreau <l.moreau@ecs.soton.ac.uk>, public-prov-wg@w3.org
Message-Id: <6B656916-4D39-487A-BF8C-E5582ED13744@inf.ed.ac.uk>
To: Stian Soiland-Reyes <soiland-reyes@cs.manchester.ac.uk>
Sounds good to me.  

To be clear, is it correct to say that the options are:

1. [status quo] - allow expanding the trigger parameter to an existential variable denoting an unknown (but definite) trigger entity
2. change the trigger parameter to be non-expandable, so that "-" means "absent trigger", as with plan and other non-expandables.

So we'll resolve this issue by taking whichever of the above has the stronger consensus?


On Aug 9, 2012, at 10:55 AM, Stian Soiland-Reyes wrote:

> I've given this a thought over night, I think that for the purpose of
> LC, we can close this issue, if we just do a strawman poll in today's
> meeting over whether it is OK to require activity start/end to have
> triggers. (which I would vote 0 for)
> On Wed, Aug 8, 2012 at 10:54 AM, Stian Soiland-Reyes
> <soiland-reyes@cs.manchester.ac.uk> wrote:
>> On Wed, Aug 8, 2012 at 9:51 AM, Luc Moreau <l.moreau@ecs.soton.ac.uk> wrote:
>>> Can you explain what you mean by activities that just 'are'?
>>> Do you mean they have no cause? Or don't know the cause?
>> An activity in PROV might be a description of an observed process,
>> rather than a record of a pre-planned activity which is already
>> understood.  What I interpret as a process depend on my assumptions of
>> what constitutes the system, etc. So if I observe that a flock of
>> birds start flying together as a single swarm, I can say that
>> swarmFlying started at 11:58 and ended at 12:04.
>> However, swarm flying is not 'caused' by anything, it is just an
>> observed pattern where we see multiple birds moving in unison. Forcing
>> this to have triggers means we have to invent trigger entities like
>> "coherentProximitiesBetweenBirds" and "avoidanceRules" which we then
>> need to explain the origin of. But any provenance trace is limited by
>> its selected boundaries of assumptions, observations and view of the
>> world; hence there would be statements which we don't make, which
>> would go 'beyond' the chosen scope. For instance in the provenance for
>> the Olympics world records, we might not include the position of the
>> moon, although it would have affected the particular tide level in the
>> river during the rowing event.
>> Similarly, a shop keeper might see 10 customers in a row buy the same
>> chocolate. What triggered this :chocolateBuying activity? Was there a
>> commercial for this chocolate? Did the shop put up a nice poster? We
>> humans are insisting on finding justifications for everything, but
>> sometimes it might just be random behaviour - this particular day, 10
>> people, choosing independently for different reasons, just happened to
>> all chose the same chocolate. So your activity is 'triggered' by your
>> own definition of it.
>> (I know this is dangerous waters, because this argument applies to
>> entities as well; it might just be the observers particular
>> characterisation that 'forms' a particular entity, and no activity for
>> wasGeneratedBy can be found).
>>> I am concerned about suddenly making triggers non-expandable
>>> (i.e. not replaceable by existential variables) because we don't know
>>> the implications of that change.
>> I understand that.  I am not giving a blank -1 to requiring triggers,
>> but I wonder if the WG has agreed on them being required to exist
>> (although they might not be stated). If we find another solution to my
>> infinite loop, I can reluctantly let them stay, although I  must admit
>> I find them quite artificial in some circumstances.
>> It is a worry that as we moved 'all the difficult bits' from PROV-DM
>> into PROV-Constraints, many of the issues that earlier caused heated
>> discussion has been silenced away, to be decided by two editors in
>> private discussions. I am not trying to reheat those kind of
>> discussions, but I am just concerned if those have been cut short
>> rather than been settled and agreed.
>> --
>> Stian Soiland-Reyes, myGrid team
>> School of Computer Science
>> The University of Manchester
> -- 
> Stian Soiland-Reyes, myGrid team
> School of Computer Science
> The University of Manchester

The University of Edinburgh is a charitable body, registered in
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Received on Thursday, 9 August 2012 09:59:51 UTC

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