Re: PROV-ISSUE-124: Constraints on Used Relation (PROV-DM and PROV-OM) [Conceptual Model]

Hi Satya,

Responses interleaved.

On 10/11/2011 07:24 PM, Provenance Working Group Issue Tracker wrote:
> PROV-ISSUE-124: Constraints on Used Relation (PROV-DM and PROV-OM) [Conceptual Model]
>
> http://www.w3.org/2011/prov/track/issues/124
>
> Raised by: Satya Sahoo
> On product: Conceptual Model
>
> The following constraints are defined for Used Relation (in PROV-DM document Oct 11, 2011):
>
> Constraint 1: "Given a process execution expression identified by pe, an entity expression identified by e, a qualifier q, and optional time t, if assertion used(pe,e,q) or used(pe,e,q,t) holds, then the existence of an attribute-value pair in the entity expression identified by e is a pre-condition for the termination of the activity represented by the process execution expression identified by pe."
>
> Issue:
> a) The above constraint may not hold for many scenarios involving Used relation. For example, if "table salt" was added by mistake to a cakeBaking PE, then Used(salt, cakeBaking PE) is true, but it is not clear what attribute-value must exist for "salt" to allow cakeBaking PE to terminate?
>
> b) Without specifying the identity, the characteristics, and how does this "attribute-value pair" relate to the Entity e itself (is it a necessary attribute-value pair for existence of e etc.) it is unclear how can we use this constraint.
>
> c) Further, is it necessary for the attribute-value to be explicitly stated prior to the start of PE instance - since with the open world assumption it may exist but not known to a provenance application before start of PE.
>
>    

We now have decided to drop this constraint. So, I guess, this answers 
your concern ;-)
> --------------
>
> Constraint 2: "Given a process execution expression identified by pe, an entity expression identified by e, a qualifier q, and optional time t, if assertion used(pe,e,q) or used(pe,e,q,t) holds, then the use of the thing represented by entity expression identified by e precedes the end time contained in the process execution expression identified by pe and follows its beginning. Furthermore, the generation of the thing denoted by entity expression identified by e always precedes its use."
>
> Issue:
> To enforce this constraint, it will be necessary for "time" (or events?) to be associated with both PE and Entity instances to derive ordering - currently association of time is optional for both PE and Entity (events is not defined).
>
>
>    

We are proposing to make a distinction between
- inferences
- so-called constraints that are there for the purpose of interpretation
- constraints that need to be enforced in the data model to be "well 
formed".

Constraint 2, is of the second kind, here to provide an interpretation 
to the data model.
It is not necessarily enforceable.

Would this address your concerns?

If so, can the issue be closed?

Thanks,
Luc

-- 
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, 7 November 2011 12:14:24 UTC