W3C home > Mailing lists > Public > public-prov-wg@w3.org > January 2012

Re: PROV-ISSUE-100 (Entity definition): Section 5.2.1 Entity [Conceptual Model]

From: Luc Moreau <L.Moreau@ecs.soton.ac.uk>
Date: Wed, 11 Jan 2012 21:49:42 +0000
Message-ID: <EMEW3|7b937b6050a291662f829dabbb9ee1d7o0ALnq08L.Moreau|ecs.soton.ac.uk|4F0E03F6.6000205@ecs.soton.ac.uk>
To: public-prov-wg@w3.org
Thanks Satya, it's now  closed.
Luc

On 11/01/12 18:22, Satya Sahoo wrote:
> Hi Luc,
> I have raised points in this issue separately reflecting changes in DM 
> (prior to SPWD). Hence, although some of my concerns in this thread 
> are not completely resolved we can close this particular issue and 
> focus on more recently raised issues.
>
> Thanks.
>
> Best,
> Satya
>
> On Wed, Nov 30, 2011 at 7:41 AM, Luc Moreau <L.Moreau@ecs.soton.ac.uk 
> <mailto:L.Moreau@ecs.soton.ac.uk>> wrote:
>
>     Hi Satya,
>
>     Our message to you earlier this month is unanswered. Since then,
>     the document has
>     substantially evolved. We now have entity and entity records, etc.
>     Furthermore, time and events are now fully discussed in section 2.
>
>     Since all your concerns have been addressed, I propose to close
>     the issue, pending review.
>     Can you confirm it is appropriate?
>
>     Regards,
>     Luc
>
>
>     On 11/07/2011 12:05 PM, Luc Moreau wrote:
>
>         Hi Satya,
>
>         Paolo and I have been discussing your issue 100. (See PM/Luc
>         comments)
>         Some of the recent accepted proposals definitely address your
>         concerns.
>         The recent changes in prov-o also, I think, answer some of
>         your queries.
>
>         I am not entirely clear what is outstanding in this issue.
>         Can you clarify for us? Can we close the issue?
>
>         Cheers,
>         Luc
>
>
>         > My review comments for Section 5.2.1 Entity in the current
>         version of the conceptual model document:
>         >
>         > 1. In PROV-DM, an entity expression is a representation of an
>         > identifiable characterized thing.
>         >
>         > Issue: Since the section heading is for Entity and the PROV DM
>         > component is Entity, I am confused why we are defining "Entity
>         > Expression" and not "Entity"?
>
>         An instance of an entity expression is syntactally written as
>         'entity', but we use the term 'entity record' (was 'entity
>         expression') to make it clear that we refer to a PROV-DM
>         construct and
>         not a thing in the world (see intro of section 5.1)
>
>         We also tried to make the distinction between the model and
>         language clearer.
>         So, we use 'records' to talk about prov-dm.
>
>         In section 2.2, we now write:
>
>          This specification also relies on a language, PROV-ASN, the
>          Provenance Abstract Syntax Notation, to express instances of that
>          data model. For each construct of PROV-DM, a corresponding ASN
>          expression is introduced, by way of a production in the ASN
>         grammar.
>
>
>         >
>         > 2. An instance of an entity expression, noted entity(id, [
>         attr1=val1,
>         > ...]) in PROV-ASN contains an identifier id identifying a
>         > characterized thing; contains a set of attribute-value pairs [
>         > attr1=val1, ...], representing this characterized thing's
>         situation in
>         > the world.
>         >
>         > Issue: When we refer to an entity in provenance assertions (in
>         > different applications), do we use the identifier to refer
>         to it or
>         > both identifier + attribute-value pairs?
>
>         Not sure I understand (in different applications).
>
>         We refer to it with its identifier.
>
>
>         >
>         > 3. The assertion of an instance of an entity expression,
>         entity(id, [
>         > attr1=val1, ...]), states, from a given asserter's
>         viewpoint, the
>         > existence of an identifiable characterized thing, whose
>         situation in
>         > the world is represented by the attribute-value pairs, which
>         remain
>         > unchanged during a characterization interval, i.e. a continuous
>         > interval between two events in the world.
>         >
>         > Issue: Are the terms "characterization interval" and "continuous
>         > interval" defined by time values? What do we mean by "continuous
>         > interval" between two events?
>
>         We assumed a partial order between events.
>         An interval between events a and b [a,b] is the set of events
>         x  such that a<= x and x<=b.
>
>         Does it really need to be defined explicitly?
>
>         PM there is a hidden issue here though: how do we get
>         agreement on event ordering? isn't this a way to sweep
>         agreement on time under the rug?
>         I am not competent enough to see this through I'm afraid but I
>         see this will creep back up on us
>
>         Luc: The reference to Lamport is crucial here.  There is
>         ordering in
>         distributed systems because the receipt of a message always
>         follows
>         its sending.
>
>          We have extended that to: the use of an entity, follows its
>          generation.  And, the end of a PE follows its start.  All event
>          ordering constraints build on those two.
>
>         Luc: it would be good to identify the events that delimit a
>         characterization interval.
>          I don't think we have a precise answer for that.
>          Start would be a generation event.
>          End could be the generation of a new entity  luc, age=10
>          terminates luc, age=9
>          End could be the destructive consumption of an entity: egg
>         broken to make a cake
>
>         Luc: events are not observable, but time is. Not global time,
>         but local time, found
>         on local clocks, more or less synchronized.
>
>
>
>         > 4. If an asserter wishes to characterize a thing with the same
>         > attribute-value pairs over several intervals, then they are
>         required
>         > to assert multiple entity expressions, each with its own
>         identifier
>         > (so as to allow potential dependencies between the various
>         entity
>         > expressions to be expressed).
>         >
>         > Issue: If a thing with same attribute-value pairs exists
>         over several
>         > time? intervals - what will be the dependencies between the
>         various
>         > entity expressions (since entity expressions = identifier +
>         > attribute-value pairs)? If they are different versions of an
>         entity,
>         > they will have distinguishing attributes other than the simple
>         > occurrence at different points of time. Further, we multiple
>         entity
>         > identifiers are used to refer to the same entity, then how do we
>         > reconcile them later?
>
>         The example of "luc in boston" in January and June has been
>         discussed extensively.
>         Theroretically, we can find distinguishing attributes, yes
>         (luc with winter clothes
>         and summer clothes). But we have no requirements that these
>         attributes are expressed.
>         So, if we have just "luc in boston" as a characterization, the
>         constraint makes sense.
>
>         PM agreed
>
>         >
>         > I believe this consideration is not required and adds a
>         layer of complexity.
>         >
>         > 5. A characterization interval may collapse into a single
>         instant.
>         >
>         > Issue: Are we referring to time values. We seem to be using
>         terms like
>         > "characterization interval", "continuous interval", "single
>         instant"
>         > etc. as surrogates for time. I suggest that we explicitly
>         use "time"
>         > if all these other terms are not distinguishable from time.
>
>         Time is a can of worms, since we can have multiple clocks, not
>         necessarily synchronised.
>
>         That's why the whole model is event based.
>
>         PM see my earlier comment. Satya has a point when he says
>         events are "surrogates for time".
>         Have no solution, but need more discussion goinf forward. This
>         issue will continue
>
>         Luc: I think that's the other way round. Observable time is an
>         approximation for events.
>
>
>         On 09/26/2011 01:58 AM, Provenance Working Group Issue Tracker
>         wrote:
>
>             PROV-ISSUE-100 (Entity definition): Section 5.2.1 Entity
>             [Conceptual Model]
>
>             http://www.w3.org/2011/prov/track/issues/100
>
>             Raised by: Satya Sahoo
>             On product: Conceptual Model
>
>             Hi,
>             My review comments for Section 5.2.1 Entity in the current
>             version of the conceptual model document:
>
>             1. In PROV-DM, an entity expression is a representation of
>             an identifiable characterized thing.
>
>             Issue: Since the section heading is for Entity and the
>             PROV DM component is Entity, I am confused why we are
>             defining "Entity Expression" and not "Entity"?
>
>             2. An instance of an entity expression, noted entity(id, [
>             attr1=val1, ...]) in PROV-ASN contains an identifier id
>             identifying a characterized thing; contains a set of
>             attribute-value pairs [ attr1=val1, ...], representing
>             this characterized thing's situation in the world.
>
>             Issue: When we refer to an entity in provenance assertions
>             (in different applications), do we use the identifier to
>             refer to it or both identifier + attribute-value pairs?
>
>             3. The assertion of an instance of an entity expression,
>             entity(id, [ attr1=val1, ...]), states, from a given
>             asserter's viewpoint, the existence of an identifiable
>             characterized thing, whose situation in the world is
>             represented by the attribute-value pairs, which remain
>             unchanged during a characterization interval, i.e. a
>             continuous interval between two events in the world.
>
>             Issue: Are the terms "characterization interval" and
>             "continuous interval" defined by time values? What do we
>             mean by "continuous interval" between two events?
>
>             4. If an asserter wishes to characterize a thing with the
>             same attribute-value pairs over several intervals, then
>             they are required to assert multiple entity expressions,
>             each with its own identifier (so as to allow potential
>             dependencies between the various entity expressions to be
>             expressed).
>
>             Issue: If a thing with same attribute-value pairs exists
>             over several time? intervals - what will be the
>             dependencies between the various entity expressions (since
>             entity expressions = identifier + attribute-value pairs)?
>             If they are different versions of an entity, they will
>             have distinguishing attributes other than the simple
>             occurrence at different points of time. Further, we
>             multiple entity identifiers are used to refer to the same
>             entity, then how do we reconcile them later?
>
>             I believe this consideration is not required and adds a
>             layer of complexity.
>
>             5. A characterization interval may collapse into a single
>             instant.
>
>             Issue: Are we referring to time values. We seem to be
>             using terms like "characterization interval", "continuous
>             interval", "single instant" etc. as surrogates for time. I
>             suggest that we explicitly use "time" if all these other
>             terms are not distinguishable from time.
>
>
>
>
>
>     -- 
>     Professor Luc Moreau
>     Electronics and Computer Science   tel: +44 23 8059 4487
>     <tel:%2B44%2023%208059%204487>
>     University of Southampton          fax: +44 23 8059 2865
>     <tel:%2B44%2023%208059%202865>
>     Southampton SO17 1BJ               email: l.moreau@ecs.soton.ac.uk
>     <mailto:l.moreau@ecs.soton.ac.uk>
>     United Kingdom http://www.ecs.soton.ac.uk/~lavm
>     <http://www.ecs.soton.ac.uk/%7Elavm>
>
>
>
Received on Wednesday, 11 January 2012 21:51:02 UTC

This archive was generated by hypermail 2.3.1 : Tuesday, 6 January 2015 21:58:11 UTC