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

From: Luc Moreau <l.moreau@ecs.soton.ac.uk>
Date: Tue, 16 Oct 2012 23:20:23 +0100
Message-ID: <EMEW3|3748d485a5ab46e1c9f05f770f0cc9efo9FNKU08l.moreau|ecs.soton.ac.uk|507DDDA7.4080300@ecs.soton.ac.uk>
To: public-prov-wg@w3.org
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
>      o
>           + 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.
>       o 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
>       o Given the different types of events, it is not sufficient to
>         have just start and end events, as suggested by the author.
>       o 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.
>       o 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:
>       o 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
>       <http://www.w3.org/2011/prov/wiki/index.php?title=ResponsesToPublicComments&action=edit&section=39>]

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, 16 October 2012 22:20:57 UTC

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