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

From: Luc Moreau <l.moreau@ecs.soton.ac.uk>
Date: Mon, 22 Oct 2012 10:50:04 +0100
Message-ID: <EMEW3|bdbc2dad6e852a8d000d702b7b2722bdo9LAo708l.moreau|ecs.soton.ac.uk|508516CC.3020607@ecs.soton.ac.uk>
To: public-prov-wg@w3.org
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:
>       o 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.
>       o 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.
>       o 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'.
>       o PROV-Constraints, in its rationale section, expands on the
>         notion of entity.
>       o 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.
>       o 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.
>       o 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.
>       o 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.
>       o 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)
>       o 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:
>       o PROV constraints
>         rationale:http://www.w3.org/TR/2012/WD-prov-constraints-20120911/#entities--activities-and-agents
>       o entity/specialization/alternate
>         definitions:http://www.w3.org/2011/prov/wiki/SpecializationAlternateDefinitions
>       o Resolution on
>         entity/specialization/alternate:http://www.w3.org/2011/prov/meeting/2012-05-03#resolution_2
>       o Key Constraints
>         definition:http://www.w3.org/TR/2012/WD-prov-constraints-20120911/#dfn-key-constraints
>       o Key-Object constraint
>         23:http://www.w3.org/TR/2012/WD-prov-constraints-20120911/#key-object
>   * Proposed Changes to the document:
>       o 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."
>       o 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 Monday, 22 October 2012 09:50:38 UTC

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