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

From: Luc Moreau <l.moreau@ecs.soton.ac.uk>
Date: Wed, 08 Aug 2012 09:51:10 +0100
Message-ID: <EMEW3|f66d9b15c655011b0a5c21a4e4c30ba0o779pC08l.moreau|ecs.soton.ac.uk|5022287E.7040406@ecs.soton.ac.uk>
To: public-prov-wg@w3.org

Hi Stian,

There are two different issues discussed in this thread.
The title suggests it is about existential triggers, which is what I 
focus on here.

Can you explain what you mean by activities that just 'are'?
Do you mean they have no cause? Or don't know the cause?

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.

Also, the default was that - was replaceable by an existential variable, 
in two cases. It seems that it is no longer the case.


On 08/08/12 09:27, Stian Soiland-Reyes wrote:
> On Mon, Aug 6, 2012 at 4:53 PM, James Cheney <jcheney@inf.ed.ac.uk> wrote:
>> Since you don't give an indication of what would resolve the issue, I'm not sure if this is a problem with PROV-DM, or with PROV-CONSTRAINTS?
>> If the latter, would making the trigger parameters non-expandable (so that you can write "-" for a missing trigger) fix the problem?  If so, I propose we do so.  (This will also require being careful about these arguments later, as for derivation and association.)
> I was just not sure if we had WG consent on the requirement of the
> trigger as I don't remember seeing a discussion about this. I think
> this is a problem with PROV-Constraints, as Prov-DM does not *require*
> the trigger, it is optional there:
>>   An end may refer to an entity, known as trigger ◊, that terminated the activity, or to an activity, known as ender ◊ that generated the trigger.
>> trigger: an optional identifier (e) for the entity triggering the activity ending;
>> ender: an optional identifier (a1) for the activity that generated the (possibly unspecified) entity (e);
> which sounds sane to me.
> However PROV-Constraints requires the trigger by existentialising (?)
> it, which I find slightly odd, because I believe activities could
> possibly be started/ended by other ways than triggers (for instance
> activities representing phenonema, which just 'are'). Or do we require
> this as a mirror to how entities must be generated by an activity, and
> bite the bullet with phantom triggers/instructions? If we have to do
> this, then I just need to be sure that this is OK even at the time
> boundaries of the activity, so it can self-start and self-terminate.
> If there are no protests, I would however prefer the - for missing
> trigger, but I know this would cause more editorial changes, similar
> to the blank "-" for the activity of wasDerivedFrom and plan of
> wasAssociatedWith. However that is what I feel is most natural, that
> both the trigger and its activity could be - for "unspecified" rather
> than "unknown"; for both wasEndedBy and wasStartedBy.
> If the inference rule is changed to imply
> wasStartedBy(_id1;a,-,-,t1,[])  and similar for wasEndedBy(), then
> this might be enough to stop the recursive looping as well. (Check!)
>> Are you also arguing for removing the wasEndedBy part of the conclusion?  If so, any objections?
> Yes, my argument is that the activity end might or might not be there.
> For an activity that as far as the provenance asserter is concerned is
> ongoing (which he has no way to say in PROV), this would be in the
> future, or it might never happen (runs forever; for instance we don't
> know if physics:expansionOfUniverse or bio:life will terminate). We
> don't know, and should not then infer it. We can infer that the
> activity is still alive at a later point (say because an entity was
> generated by the activity), and hence know that there is no wasEndedBy
> earlier than that point, but we don't know there will be an
> wasEndedBy.

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 08:51:43 UTC

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