Re: PROV-ISSUE-67 (single-execution): Why is there a difference in what is represented by one vs multiple executions? [Conceptual Model]

JIm

we have established that isDerivedFromInMultipleSteps is also transitive. I hope this is fine.

The point of having the relation is that, as Luc explained here below, in this case the "pe introduction rule"(*) should not be used.
In other words, isDerivedFromInMultipleSteps simply means that, according to the asserter, more than one pe is required to explain 
the derivation (but we don't know how many).

I can see that your objection is valid, however, in the sense that I can make up one single pe that encompasses an arbitrary number 
of steps.
The problem is that we haven't said anything about the nature of the activity represented by a pe. Unless we say something about 
their granularity and composition, any pe can represent any aggregation of "elementary" activities.

-Paolo

(*) if*isDerivedFrom(e1,e0)*holds, then there exists a process execution*pe*, and roles*r0*,*r1*, such 
that:*isGeneratedBy(e1,pe,r1)*and*uses(pe,e0,r0)*.


8/2/11 3:08 AM, Myers, Jim wrote:
>> It's not that pe is atomic or not. It's that there is a tight link between
> the derivation and  the process execution.
>
>> isDerivedFromInMultipleSteps is silent about that link.
> If B isDerivedInMultipleSteps from A, can't I (a second witness) always make up a single process that encompasses all steps? Would it then be OK (for me, the second witness making up this account) to claim a direct B isDerivedFrom A. Then I can do transitive closure over such relationships? And then recognize that there were multiple steps, thus making isDerivedInMultipleSteps transitive too?
>
>> I am not trying to infer derivation beyond transitive closures.
> I don't see how the definitions given allow one to be transitive and one not to be. If the only difference between the two was an implication of how much the witness knew about what happened (one step or multiple), but both were transitive, I wouldn't be confused (I might still argue that we don't need the distinction).
>
> Cheers,
>   Jim
>
>
> Regards,
> Luc