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

On Oct 22, 2012, at 5:50 AM, 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.


+1

-Tim

> 
> 
>> 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
>