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PROV-ISSUE-473 (generating-activity): Unique generation events and activities [prov-dm-constraints]

From: Provenance Working Group Issue Tracker <sysbot+tracker@w3.org>
Date: Thu, 09 Aug 2012 14:35:04 +0000
Message-Id: <E1SzTpI-0002lS-Jw@tibor.w3.org>
To: public-prov-wg@w3.org
PROV-ISSUE-473 (generating-activity): Unique generation events and activities [prov-dm-constraints]


Raised by: Simon Miles
On product: prov-dm-constraints

As requested, I'm submitting an issue where I feel a PROV-Constraints review comment of mine is not completely answered.

My original comment:
   > Unique generations
   > -----------
   > C. Immediately following Inference 12, the text says "the entity
   > denoted by e2 is generated by at most one activity (see Constraint
   > 27". The Remark below repeats this, "at most one activity could
   > generate the entity e2." 
   > This seems wrong. Constraint 27 says that e2 is generated by only one
   > generation event, not by only one activity. The distinction between
   > these is important. In the primer's example, there is an activity
   > ex:compile which is decomposed into steps ex:compose and
   > ex:illustrate. While there is only one (implicit) generation event for
   > entity ex:chart1, both ex:compile and ex:illustrate can be asserted to
   > have generated the entity. 

Response from editors:
 > Constraint 27 indeed says that there is a single generation event 
 > and constraint 26 says that the id is a key for a wasGeneratedBy
 > which implies that there is a single activity.
 > In the primer, you assert:
 >   wasGeneratedBy(ex:chart1, ex:compile,  2012-03-02T10:30:00)
 >   wasGeneratedBy(ex:chart1, ex:illustrate,  2012-03-02T10:30:00)
 > This is invalid.
 > One way to address this is to maintain two levels of abstraction for
 > both activities and entities.
 >  wasGeneratedBy(ex:chart1_abstract, ex:illustrate,  2012-03-02T10:30:00)
 >  specializationOf(ex:chart1,ex:chart1_abstract)  // or similar.

This response explains why the current constraints do not allow what I described, but not why they are meaningful. The questions below hopefully articulate my concerns.

 1. The response suggests that the invalidity of the primer example is due to it describing multiple levels of abstraction for a single entity. Why should this be invalid? Why has validity got anything to do with levels of abstraction? As far as I can see, this is not stated or explained in PROV-Constraints.

 2. As ex:chart1_abstract and ex:chart1 are exactly the same entity with exactly the same attributes and generated at the same instant, then why would we want statements implying one was more abstract than the other? Isn't this at least misleading?

I also have one related follow-on question:

 3. Even if we do use the specialization approach to get around the constraints as suggested, there can only be one entity per generation event. If something is described at multiple levels of abstraction, then does that necessitate a unique generation event for each level (each entity)? If so (as appears), why? When I create the first version of a document, in the same instant I create both "doc" and "docV1". How do I describe that the event creating one is the "same" event that created the other? It is surely the "same" event in some strong, objective sense, even if we prefer to describe it using a different identifier for each entity.

Received on Thursday, 9 August 2012 14:35:10 UTC

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