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Re: PROV-ISSUE-462 (entity-definition-precision): Definition o entity may be too liberal [prov-dm]

From: Khalid Belhajjame <Khalid.Belhajjame@cs.man.ac.uk>
Date: Tue, 23 Oct 2012 09:52:37 +0100
Message-ID: <CAANah+Hc25fcuOSdNAhSJokcHMa0buH3zbXs5xkO9wBvZssMLw@mail.gmail.com>
To: Luc Moreau <l.moreau@ecs.soton.ac.uk>
Cc: public-prov-wg@w3.org
The response to this issue is thorough and I think we should go ahead with it.
However, I think that the reviewer is right: identifying what an
entity is may be difficult for prov users (compared for example to
Activity which is simple and clear), and I am anticipating that the
entity concept will be mis-used more than others.

Thanks, khalid

On 22 October 2012 10:50, Luc Moreau <l.moreau@ecs.soton.ac.uk> wrote:
> Dear all,
> I have drafted a response to the following issue. See
> http://www.w3.org/2011/prov/wiki/ResponsesToPublicComments#ISSUE-462_.28Definition_of_Entity.29
>  I will implement the changes once I have a confirmation
> the group is happy with them, and they satisfactorily address the issue.
> ISSUE-462 (Definition of Entity)
> Original email:
> http://lists.w3.org/Archives/Public/public-prov-comments/2012Jul/0009.html
> Tracker: http://www.w3.org/2011/prov/track/issues/462
> Group Response:
> The term 'entity' is intentionally defined in a liberal manner to avoid
> restricting users expressivity. Obviously, it shouldn't be too liberal,
> otherwise it would be all encompassing, without clear semantics.
> The term 'entity' (and associated notions such as 'alternate',
> 'specialization') have been the subject of intense debate by the Working
> Group, and the definition reflects the compromise reached by the Working
> Group.
> The term 'aspect' is not used here with a technical meaning and should be
> understood with its dictionary meaning 'A particular part or feature of
> something'.
> PROV-Constraints, in its rationale section, expands on the notion of entity.
> While an object/thing may change over time, an entity fixes some aspects of
> that thing for a period of time (in between its generation and
> invalidation). As opposed to other models of provenance (such as OPM), an
> entity is not an absolute state snapshot. Instead, it is a kind of partial
> state, just fixing some aspects. The rationale for this design decision is
> that it is quite challenging to find absolute state snapshots that do not
> change: the location of a file on a cloud changes, the footer of this Web
> page changes (as more people access it), etc. Hence, by allowing some
> aspects (as opposed to all) to be fixed, the PROV concept of 'entity' is
> easy to use.
> We distinguish an 'aspect' from an 'attribute'. An attribute-value pair
> represents additional information about an entity (or activity, agent,
> usage, etc). In the case of an entity, attribute-value pairs provide
> descriptions of fixed aspects. So, the term 'aspect' refers to properties of
> the thing, whereas the term 'attribute' refers to its description in PROV.
> PROV does *NOT* assume that all fixed aspects are described by
> attribute-value pairs. So, there may be some fixed aspects that have not
> been described. Obviously, without description, it's difficult to query or
> search over them.
> According to PROV Constraint key-object (constraint 23), an entity has a set
> of attributes given by taking the union of all the attributes found in all
> descriptions of that entity. In other words, PROV does not allow for
> different attribute-value pairs to hold in different intervals for a given
> entity.
> The attribute-value pairs of an entity provide information for some of the
> fixed aspects of an entity.
> This point may not have been clear, and requires text modification. (see
> below)
> A specific attribute of an entity is its identity. It is also assumed that
> it holds for the duration of the entity lifetime.
> This point may not have been clear, and requires text modification. (see
> below)
> References:
> PROV constraints rationale:
> http://www.w3.org/TR/2012/WD-prov-constraints-20120911/#entities--activities-and-agents
> entity/specialization/alternate definitions:
> http://www.w3.org/2011/prov/wiki/SpecializationAlternateDefinitions
> Resolution on entity/specialization/alternate:
> http://www.w3.org/2011/prov/meeting/2012-05-03#resolution_2
> Key Constraints definition:
> http://www.w3.org/TR/2012/WD-prov-constraints-20120911/#dfn-key-constraints
> Key-Object constraint 23:
> http://www.w3.org/TR/2012/WD-prov-constraints-20120911/#key-object
> Proposed Changes to the document:
> http://www.w3.org/TR/prov-dm/#entity.attributes: instead of "representing
> additional information about this entity." write "representing additional
> information about the fixed aspects of this entity."
> http://www.w3.org/TR/prov-dm/#term-identifier: add the following.
> Entity, Activity, and Agent have a mandatory identifier. Two entities (resp.
> activities, agents) are equal if they have the same identifier.
> Generation, Usage, Communication, Start, End, Invalidation, Derivation,
> Attribution, Association, Delegation, Influence have an optional identifier.
> Two generations (resp. usages, communications, etc.) are equal if they have
> the same identifier.
> Luc
> On 07/25/2012 08:16 AM, Provenance Working Group Issue Tracker wrote:
> PROV-ISSUE-462 (entity-definition-precision): Definition o entity may be too
> liberal [prov-dm]
> http://www.w3.org/2011/prov/track/issues/462
> Raised by: Paul Groth
> On product: prov-dm
> This is the issue for
> http://lists.w3.org/Archives/Public/public-prov-comments/2012Jul/0009.html
> from Jacco van Ossenbruggen
> --
> 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 08:53:08 UTC

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