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Re: PROV-ISSUE-499: Data Model Section 2.1.1, semantics [prov-dm]

From: Khalid Belhajjame <Khalid.Belhajjame@cs.man.ac.uk>
Date: Tue, 23 Oct 2012 09:33:00 +0100
Message-ID: <CAANah+GmH4Jdb+WOdtcsc0+WRVPYobGrYLTUDnxYPP49CcDvXA@mail.gmail.com>
To: Luc Moreau <l.moreau@ecs.soton.ac.uk>
Cc: public-prov-wg@w3.org
The response made to issue 499 addresses all the concerns raised by
the reviewer.
So I think we can go ahead with it.

Thanks, khalid

On 16 October 2012 23:20, Luc Moreau <l.moreau@ecs.soton.ac.uk> wrote:
> Dear all,
>
> I am adding this proposed answer to the list of answers under review.
> Feedback welcome.
>
> ISSUE-499 (Generation vs Activity)
>
> Original email:
> http://lists.w3.org/Archives/Public/public-prov-wg/2012Sep/0089.html
> Tracker: http://www.w3.org/2011/prov/track/issues/499
> Group Response
>
> The author states It is not clear why it is necessary to define terms for
> discrete points in time within the PROV model. If activities already have
> start and end times, isn't that sufficient?.
> As indicated in prov-constraints, PROV is implicitly based on a notion of
> instantaneous events. Five of them are identified,
> start/end/generation/usage/invalidation.
> These events are of interest because they mark a "change of state" in the
> world: an activity is started/end, an entity is generated/used/invalidated.
> These types of events matter because they enable or disable the occurrence
> of further events. For instance, before generation, an entity cannot be
> used, but it can after its generation, ... until its invalidation.
> Those events always involve an activity and an entity:
>
> start and end of an activity with respect to a trigger
> generation/usage/invalidation of an entity by an activity.
>
> Each type of event enables or disables the occurrence of specific types of
> events:
>
> Start of a:
>
> No event with a can precede start of a, event with a can follow start of a
>
> End of a:
>
> Event with a can precede end of a, event with a cannot follow end of a
>
> Generation of e:
>
> Event with e cannot precede generation of e, event with e can follow
> generation of e
>
> Invalidation of e:
>
> Event with e can precede invalidation of, event with e cannot following
> invalidation of e
>
> Usage of e by a:
>
> "influence" of e can "show" after usage by a, but cannot "show" before usage
>
> Given the different types of events, it is not sufficient to have just start
> and end events, as suggested by the author.
> In PROV activities "occur". They do "stuff". They act upon and with
> entities. The activities are involved in the generation and usage of
> activities: as indicated above, an event always occurs in the context on an
> activity.
> If, for some application, it is useful to see the creation of entities as
> having a duration, this indeed can be modelled by an activity with a
> duration. But what we care about, from a provenance viewpoint, is when the
> entity is actually created, which we then refer as generation. This cannot
> be modelled by an activity. The generation (event) is in the model the
> relation between an activity and an entity.
>
> References:
>
> PROV-constraints events:
> http://www.w3.org/TR/2012/WD-prov-constraints-20120911/#events
>
> Changes to the document: To implement
> Original author's acknowledgement:
>
> [edit]
>
>
>
>
>
>
> On 10/09/12 09:32, Provenance Working Group Issue Tracker wrote:
>
> PROV-ISSUE-499: Data Model Section 2.1.1, semantics   [prov-dm]
>
> http://www.w3.org/2011/prov/track/issues/499
>
> Raised by: Luc Moreau
> On product: prov-dm
>
>
>
> http://www.w3.org/2011/prov/wiki/LC_Feedback#Data_Model_Section_2.1.1.2C_semantics
>
> ISSUE-463
>
> There seems to be significant semantic conflicts in the definitions of a few
> terms: - Activity: "something that occurs over a period of time  may
> include  using or generating entities" - Generation: "the completion of
> production" - Usage: "the beginning of utilizing"
>
> Based on the definition for Activity, usage and generation appear to be
> activities, but the separate definitions for those terms clearly indicate
> they are discrete points in time (at the beginning or end of an activity)
> and are not activities themselves. This is further confused by Figure 1 and
> Table 2, which list usage and generation as relations and not timepoints.
>
> It is not clear why it is necessary to define terms for discrete points in
> time within the PROV model. If activities already have start and end times,
> isn't that sufficient?
>
> If these distinctions are important, I would recommend using different terms
> in the definitions and examples to break the circularity between them.
>
>
> [edit]
>
>
>
>
> --
> 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 Tuesday, 23 October 2012 08:33:32 UTC

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