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

Graham,
I think the key thing is not whether there are atomic PEs (and Bobs) per se, but that if there's more than one level of granularity that makes sense, it would be good to have a definition of derivation that does not depend on which you choose. I think this is the argument behind not inferring derivation from used-PE-generated - there are cases where thinking of that PE as multiple sub-PEs would show that there is no direct connect between the input and output. My/your(?) concern about transitivity is analogous - if viewing a Bob at finer granularity shows that there's no direct link, derivation becomes asserter dependent. I don't think this quite drives us to needing atomic PEs and Bobs to build since the problem is really that going just a bit finer may alter the graph structure. For example, with the PE example where used occurs after generation, simply splitting the PE in two would show that the output is generated by the first PE and the only connect from the output to the input is via the forward-in-time link between PE1 and PE2. If we break PE1 and PE2 further, we could make longer and longer chains, but the graph 'shape' - the fact that the output and input are only connected via a forward-in-time link doesn't change and hence what the ultimate granularity might be is not so relevant. Same thing with aggregate Bobs - once we find that a one process created B.1 and the second used B.2, unless B.1 is connected to B.2 by some PE, there is no continuous chain between the final Bob and the initial one that would justify transitivity. Again, how far you might be able to divide a Bob is not directly relevant if finer breakdown doesn't change the graph structure. So - I hope this allows us to avoid having to identify what the ultimate atomic level of reality might be :-)

 Jim

> -----Original Message-----
> From: public-prov-wg-request@w3.org [mailto:public-prov-wg-
> request@w3.org] On Behalf Of Graham Klyne
> Sent: Thursday, August 04, 2011 4:05 AM
> To: Luc Moreau
> Cc: public-prov-wg@w3.org
> Subject: Re: PROV-ISSUE-67 (single-execution): Why is there a difference in
> what is represented by one vs multiple executions? [Conceptual Model]
> 
> I'm not fully up to speed on this discussion, but there's a consideration I wanted
> to suggest.  The distinction between single- and multiple process execution
> steps seems to assume that at some level there are distinct atomic operations.
> 
> But consider a dataset stored on a medium that is subject to degradation over
> time.  What is the atomic item of "process execution" in this degradation
> process? Individual state changes at the atomic/molecular level?  (I think not.)
> 
> SO: do we need a model that allows a mereological interpretation of process
> execution?
> 
> (I think this also overlaps the discussion of ISSUE 66)
> 
> #g
> --
> 
> 
> 
> Luc Moreau wrote:
> > Hi Simon,
> >
> > If I understand you correctly, you are suggesting that the following
> > two assertions hold together.
> >
> > isGeneratedBy(e5,pe5,out)
> > isGeneratedBy(e5,pe4,out)
> >
> > But this is not legal, since it is stated that one BOB is generated by
> > at most one process execution.
> >
> > What you are suggesting should be encoded in a separate account
> > (though we have not defined this yet!).
> > A one-step derivation then expands to one process execution in a given
> > account.
> > In a separate account, there may be a multi-step derivation between
> > the same two BOBs and it would expand into multiple process
> > executions.
> >
> > Does it make sense?
> > Regards,
> >
> > Luc
> >
> >
> > On 07/29/2011 05:52 PM, Provenance Working Group Issue Tracker wrote:
> >> PROV-ISSUE-67 (single-execution): Why is there a difference in what
> >> is represented by one vs multiple executions? [Conceptual Model]
> >>
> >> http://www.w3.org/2011/prov/track/issues/67

> >>
> >> Raised by: Simon Miles
> >> On product: Conceptual Model
> >>
> >> By the definition, "a process execution represents an identifiable
> >> activity". This does not seem to preclude one process execution
> >> assertion denoting, at a coarse granularity, the same events in the
> >> world denoted by multiple process executions in other assertions.
> >>
> >> If so, then in the File Scenario example, I could add a
> >> coarse-grained process execution representing the whole e1-to-e5 activity:
> >>    processExecution(pe5,collaboratively-edit,t)
> >>    uses(pe5,e1,in)
> >>    isGeneratedBy(e5,pe5,out)
> >>
> >> But then Section 5.5.2 distinguishes between "a single process
> >> execution" and "one or more process executions". Following the
> >> argument above, these could represent exactly the same occurrences in
> >> the world.
> >>
> >> So there is no difference between what is denoted by one and multiple
> >> process executions, and so no difference between isDerivedFrom and
> >> isDerivedFromInMultipleSteps as described. Whether e5 was derived
> >> from
> >> e1 appears to me to be entirely independent of how many process
> >> executions were involved.
> >>
> >>
> >>
> >>
> >>
> >
>

Received on Thursday, 4 August 2011 15:01:53 UTC