Re: PROV-ISSUE-50 (Ordering of Process): Defintion for Ordering of Process [Conceptual Model]

Hi Luc,
I would like to re-raise this issue since the two properties defined in
PROV-DM, "wasInformedBy" and "wasScheduledAfter" do not represent the
original property for ordering process executions that was agreed to by the
provenance incubator group and also during the first F2F [1].

I believe there are primarily two dimensions/constraints for ordering
process executions:
a) Two PEs are scheduled (by agent/user) to execute in particular order at
specific time instants, which we can represent as *time-based ordering of
PEs*. Of course, additional information about which agent/user started or
stopped the PEs can be specified, but the time value primarily define the
ordering of the PEs.

b) A PE pe1 is designed to initiate/start a second PE pe2 (due to some
condition being satisfied for example a specific state was reached or some
entity became available), which we can represent as a *control-based
ordering of PEs*. This ordering of process cannot be effectively captured by
time-based ordering, since pe1 may still be executing while pe2 starts.

Both these cases are captured by the property "wasPrecededBy" (the
corresponding property in opposite direction can be "wasSucceededBy") where
the PEs were ordered according to their time of start/stop or explicit
start/stop by another PE.

Some specific comments on the current PROV-DM document Section 5.3.6
Ordering of Process Executions
=====
1. An information flow ordering expression is a representation that a
characterized thing was generated by an activity, represented by a process
execution expresion, before it was used by another activity, also
represented by a process execution expression.

Issue: This is a particular case of "time-based ordering", there can
multiple others. For example,

a) We can have the provenance assertions about two PEs Pe1 and Pe2: Pe1 was
stopped at time instant t1 and Pe2 started at time instant t2 and t2 > t1.
Hence Pe2 wasPrecededBy Pe1

b) Similarly, we have provenance assertions about two PEs Pe1, Pe2 and an
Entity e1: Pe1 used e1 at time t1 and PE2 used e1 at time t2 and t2 > t1,
hence (start of) Pe2 wasPrecededBy (start of) Pe1.

My suggestion to just create a single generic property for ordering of PEs
(Khalid had suggested using PEs instead of Process) and allow specific
provenance application to create more specialized PE ordering properties
according to their requirements.

2. According to the current definition of "wasScheduledAfter" we cannot
assert that one PE was scheduled after another PE if we don't have
information about the agent associated with the PEs. Further, the name of
the property seems to refer to the intended ordering of PEs rather than
actual execution of PEs - a workflow specification may have "scheduled" Pe1
to execute "after" Pe2, but during the workflow run, Pe2 may have executed
before Pe1?

Overall, I am not sure why we need two very special cases of PE ordering
property instead of using a generic "wasPrecededBy" (or "wasSucceededBy")
property that can be specialized as needed by different provenance
applications.

Thanks.

Best,
Satya

[1]
http://www.w3.org/2011/prov/wiki/ConsolidatedConcepts#Ordering_of_process_execution

On Fri, Sep 23, 2011 at 8:04 AM, Luc Moreau <l.moreau@ecs.soton.ac.uk>wrote:

>
> Hi Satya,
>
> Issue has been closed pending review, with the latest document version.
> Feel free to reopen if not appropriate.
>
> Luc
>
>
> On 27/07/2011 02:51, Provenance Working Group Issue Tracker wrote:
>
>> PROV-ISSUE-50 (Ordering of Process): Defintion for Ordering of Process
>> [Conceptual Model]
>>
>> http://www.w3.org/2011/prov/**track/issues/50<http://www.w3.org/2011/prov/track/issues/50>
>>
>> Raised by: Satya Sahoo
>> On product: Conceptual Model
>>
>> I am not sure where did we get the currently listed definition of
>> "Ordering of Process" - it is neither listed in the original provenance
>> concept page [1] nor in the consolidated concepts page [2].
>>
>> I had proposed the following definition:
>> "Ordering of processes execution (in provenance) needs to be modeled as a
>> property linking process entities in specific order along a particular
>> dimension (temporal or control flow)"
>>
>> [1]http://www.w3.org/2011/**prov/wiki/**ConceptOrderingOfProcesses<http://www.w3.org/2011/prov/wiki/ConceptOrderingOfProcesses>
>> [2] http://www.w3.org/2011/prov/**wiki/ConsolidatedConcepts#**
>> Ordering_of_process_execution<http://www.w3.org/2011/prov/wiki/ConsolidatedConcepts#Ordering_of_process_execution>
>>
>>
>>
>>
>>
>
>