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Re: Some thoughts about the revised provenance Model document

From: Graham Klyne <Graham.Klyne@zoo.ox.ac.uk>
Date: Wed, 19 Oct 2011 16:44:33 +0100
Message-ID: <4E9EF061.6030706@zoo.ox.ac.uk>
To: "Myers, Jim" <MYERSJ4@rpi.edu>
CC: Paul Groth <p.t.groth@vu.nl>, 'W3C provenance WG' <public-prov-wg@w3.org>, "Luc Moreau (L.Moreau@ecs.soton.ac.uk)" <L.Moreau@ecs.soton.ac.uk>
Jim,

Yes, we seem to be converging.

If there's a consensus that it's important to be able to use the provenance 
model (alone) to refer to things like "the image with subject X", then I'd agree 
that attributes as described are a reasonable way to do this, and I'm prepared 
to back down on this point.  My own take was that any of the common referencing 
mechanisms could be used, including using a URI, and that the provenance model 
should focus on actually representing the provenance information.  Simply adding 
the notion of attributes is a relatively small overhead, which is probably 
useful in a majority of cases, and fits quite well with an RDF representation. 
For me, the compelling case you make is that the attributes make it easier to 
convert to/from other formats for representing provenance.

But I think that worrying about "non-characterizing attributes", and requiring 
mechanisms to distinguish them, is an unnecessary complication at several levels.

I agree with you that we don't need to worry about "incidental" fixed 
attributes.  I'd take the view that any attributes mentioned in an entity 
expression are defined to be characterizing for the purposes ascribing 
provenance to that entity.  If a user creates a redundant expression containing 
incidental attributes, then what harm?

I need to find time to revisit the model document to turn this into a formal 
issue.  When I do so, I'd plan to include a change proposal.  Meanwhile, I don't 
think this should be having too much impact on developing other areas.

#g
--

On 18/10/2011 15:45, Myers, Jim wrote:
>
>
>> -----Original Message-----
>> From: Graham Klyne [mailto:graham.klyne@zoo.ox.ac.uk]
>> Sent: Monday, October 17, 2011 1:48 PM
>> To: Myers, Jim
>> Cc: Paul Groth; 'W3C provenance WG'
>> Subject: Re: Some thoughts about the revised provenance Model document
>>
>> On 04/10/2011 15:24, Myers, Jim wrote:
>>>> To the extent that provenance assertions actually
>>>> *are* static attributes of that entity, ...
>>>
>>> - how do you make such assertions if static attributes aren't in the model?
>>
>> Jim,
>>
>> Short answer: use a new predicate.
>>
>> For example, if w is weather in London, then w1 = ( w such that
>> On20111017(w) ) might be the weather in London on 2011-10-17.  Of
>> course, the predicate can alternatively be construed as an attribute+value,
>> which is close to what I alluded to when I said "To the extent that
>> provenance assertions actually *are* static attributes of that entity".  (I think
>> Quine discussed this kind of duality between predicates and properties of
>> things in one of his assays.)
>>
>> ...
>
>
>> But I detect two different possible questions here:
>>
>> - how do you make such assertions using the model if static attributes aren't
>> in the model?
>>
>> and
>>
>> - how do you make such assertions by any means if static attributes aren't in
>> the model?
>>
>> And I realize my previous answer only addresses the latter case.
>
> Yes - I'm concerned about the former - can we cover use cases with just the model itself. I think both you and Satya make good arguments that, if you're willing to go beyond the model, you can do a better/more general job of modeling how an entity is fixed. I don't want to preclude that, but I'm concerned that if there's not an in-model option, we haven't really provided provenance interoperability (some agreement would be required between parties for one to generate provenance and the other to answer questions with it that correspond to our use cases (examples below).
>
>>
>>> If I understand your concerns correctly, they are partly due to
>>> language about entities being 'defined by' fixed attributes. I don't
>>> think it would be problematic, and in fact would probably agree with
>>> an alternate description that talks about entities being
>>> characterizations of things that limit their behavior over time
>>> (statements about object identities and states/characteristics have to
>>> remain true...)  and that characterizing attributes are a/the way in
>>> the provenance model to allow interchange of information about those
>>> limits (i.e. such attributes are not theoretically a defining aspect
>>> of entities but, in order to allow interchange and practical use of
>>> provenance information without knowledge of external object
>>> definitions/functionality, fixed attributes are defined.)
>>>
>>> Does this get us to a conceptual consensus?
>>
>> That's certainly closer to what I had in mind.  In reading your earlier
>> response, I realized I had not one but two niggles with the current
>> formulation:
>>
>> (1) the need to distinguish between characterizing and non-characterizing
>> attributes
>>
>> (2) The use of attributes at all.
>>
>> I read your above formulation as allowing us to talk about characterizing
>> attributes while completely ignoring other attributes, which AFAICT are
>> irrelevant to description of provenance, addressing my concern (1)
>>
>
> I think I agree re: (1) but to clarify: I've heard two senses of non-characterizing - one where non-characterizing means 'incidental' - my height is fixed but I'd still be 'me' if it were different, and one where it means non-fixed. My sense is that we don't need to distinguish the first sense - whether a fixed property is characterizing or incidental is irrelevant to it being useful for discovering an instance and we just need a neutral term. Non-fixed attributes, such as my location, and the interest some have expressed in being able to record them, ie. say that Jim has a location without giving a value (with Jim-in-NY being another ivp/complementary entity where it is fixed), seems like it can be pushed out of scope - while one might want to infer that Jim complement of Jim-in-NY implies that Jim has a mutable location, we don't lose any functionality requiring people to frame a query about where Jim was at a specific time/point in provenance as a query about Jim being t

he complement of an entity with a fixed location.
>> ...
>>
>> My concern (2) is more subtle (and I could more easily let it be).
>>
>> The goal that I perceive is to be able to say that some entity, say e1, is a
>> characterization of a dynamic entity, say e, that allows us to make some
>> provenance assertions whose truth is not ephemeral.  What I don't see is
>> why one needs to know exactly how the constraints on e that correspond to
>> e1 are determined.  If one makes a (true) provenance assertion about e1,
>> then it seems to me that the necessary constraints exist for the provenance
>> assertion about e1 to be true.  My assumption is that the specific nature of
>> the constraints is application or context dependent, and does not need to be
>> part of the core provenance model.
>
> I think we need this goal (to be able to make non-ephemeral statements about e) but I think the use of something like e1 has an additional goal - to record how e changed. If I just want to record unambiguously that a document was edited, I'd like to just say document e participatedIn editingPE, without creating an e1 or e2 for the before/after entities. (I'm not sure if that is currently consistent with how we've defined participation - I think it was at one point). To me, the value of making e1 and e2 explicit is to have a place where I can unambiguously talk about the text in those versions. e1 hasText "Hello" and e2 hasText "Hello World".
>>
>> For comparison: If we assert that a particular document d3 was derived
>> from some datasets d1 and d2, we accept that as an assertion, without
>> having to care about how that knowledge was obtained.  I'm applying a
>> similar standard to the nature of constraints used to determine views (IVPs)
>> for which provenance can be asserted.
>
> I think this would be the case where I want to just say e participatedIn editingPE - that assertion implies that there were before and after versions that differ in aspects affected by editingPE, but if I don't think the attributes of those versions are of interest, I wouldn't even assert them.
>
> TO address the point that some people may have better out-of-band mechanisms to characterize entities, I think the prov model should still allow one to id e1 and e2 without attributes - someone who is constrained to only use the prov model itself can't make as much use of those (I guess they could return the product of e being edited, but they couldn't return the version with given text or length, etc if those weren't attributes), but there's no reason to require attributes to be asserted by parties that have their own interoperability agreements about the nature of entities they're describing.
>>
>> Having said that, I note you mentioned in another message that the notion
>> of attributes was needed to satisfy the provenance challenge.  I'm not aware
>> of the
>> details:  maybe there's a specific use-case here that could change my
>> perspective on this...
>
> Simple things - the Challenge required on group to read provenance from another group and answer questions like (these are not the real challenge examples) "what was derived from the image withSubject x)" or "which products from stage2 with dc:creator Bob were used to create new files". If you envision OPM as a model, not a syntax, and groups with text, XML, and RDF implementations you can start to see the problem. The model to mapping syntax covers how to read artifacts and processes from the serialized forms, but without attributes in the model, there was no standard/predefined way to find which image was of subject X, or what processes were 'stage2' or which files had dc:creator Bob. Having the idea in the model that artifacts and processes could have key/value attributes and then describing how key/value attributes are serialized to the different formats enabled the groups to read each other's provenance and answer the queries. (In reality, before we had attributes in O

PM, everyone looked at the serializations and figured out how to map and just 
extended the model on their own to get the work done, but in doing so we 
recognized that we had done something outside the model to answer the queries.)
>
> Cheers - and apologies for being in and out of the discussions,
>   Jim
>>
>> #g
>> --
>>
>>>> then the existence of static attributes
>>>> (in the style of "characterizing attributes") may be inferred.  In this
>> respect,
>>>> the static attributes are a consequence rather than a defining aspect of
>> the
>>>> existence of meaningful provenance information.
>>>>
>>>> #g
>>>> --
>>>>
>>>>> Graham Klyne wrote:
>>>>>> Jim,
>>>>>>
>>>>>> If I understand you correctly, the significance of attributes is for
>> discovery
>>>>>> of of related resources.
>>>>>>
>>>>>> My understanding is that the primary purpose of provenance is to
>>>> establish a
>>>>>> basis for trust, a reason to believe (or not) some information that is
>>>> presented
>>>>>> about some subject. It's not clear to me what need there is to use
>>>> attributes
>>>>>> for resource discovery to achieve this end. (But I may well be missing
>>>>>> something here.)
>>>>>>
>>>>>> So, on this basis, there may be perfectly good reasons to have defined
>>>>>> attributes and values for discovery purposes, I'm not seeing why they
>> are
>>>> needed
>>>>>> to achieve the goals of *provenance* information.
>>>>>>
>>>>>> (But it's getting late here, and maybe I'm missing some key point in
>> your
>>>>>> message.)
>>>>>>
>>>>>> In summary: I think your concerns are reasonable, but what makes
>> them
>>>> in scope
>>>>>> specifically for *provenance* information?
>>>>>>
>>>>>> #g
>>>>>> --
>>>>>>
>>>>>> On 29/09/2011 18:44, Myers, Jim wrote:
>>>>>>> Graham,
>>>>>>>
>>>>>>> How would we use provenance to find, for example, how Luc got to
>>>> Boston? It's
>>>>>>> clear if we have fixed attributes for name and location such that we
>>>> could
>>>>>>> query for an entity with name Luc that has an ivpOf relationship with
>> an
>>>>>>> entity in Boston and then look at the provenance from there. How
>> would
>>>> it
>>>>>>> work without fixed attributes in the prov model? I'm guessing that
>>>> you're
>>>>>>> thinking that we can find those attributes outside the language
>>>> somewhere
>>>>>>> (e.g. non-prov RDF statements) but what are the minimal
>> requirements
>>>> there
>>>>>>> and what language/models exist that meet them? Can we only model
>>>> provenance
>>>>>>> of things for which ontologies have been developed? Presumably it
>> has
>>>> to be
>>>>>>> possible to associate descriptive metadata with the entities through
>>>> some
>>>>>>> path (what relationship(s)?)? And it has to be clear which metadata
>> is
>>>> fixed?
>>>>>>> You mention being able to infer across ivpOf relationships - is there
>> one
>>>> set
>>>>>>> of inference rules for all possible descriptive metadata? Or do we
>> need
>>>> to be
>>>>>>> able
>>>>>
>>>>>> to distinguish further between types of metadata?
>>>>>>> -->   As you can probably guess from the questions above, I'm
>> concerned
>>>> that
>>>>>>> kicking fixed attributes out will end up being more complex and place
>> a
>>>>>>> higher burden on users than keeping them in, but I may be
>>>> misunderstanding
>>>>>>> how such an alternative would work. Part of that concern is that I
>> think I
>>>>>>> hear that modeling experts in this group can handle defining classes
>> for
>>>>>>> different types of entities that would allow discovery by attribute, but
>>>> I'm
>>>>>>> concerned that being able to do this becomes a requirement for using
>>>>>>> provenance (versus asserting entities defined solely by
>> attributes(entity,
>>>>>>> name=Luc) or perhaps in a mixed mode (e.g. an entity representing
>> Luc
>>>> that
>>>>>>> 'hasBaseType' foaf:person and one representing him in Boston that
>> also
>>>>>>> hasBaseType foaf:person and location=Boston as a fixed attribute.)
>>>> Again -
>>>>>>> perhaps I'm misunderstanding how discovery based on descriptive
>>>> information
>>>>>>> could be done if we don't have fixed characterizing attributes in the
>> prov
>>>>>>> standard....
>>>>>>>
>>>>>>> Jim
>>>>>>>
>>>>>>>> 3. Do we need to model "Characterizing attributes"?
>>>>>>>>
>>>>>>>> The notions of "characterizing attributes" have developed to derive
>> the
>>>>>>>> relationship between different entities that are views of some
>>>> common
>>>>>>>> thing in the world. I am not convinced that we need to model these
>>>>>>>> attributes, and I'm not sure the way they are modelled can
>> necessarily
>>>> apply
>>>>>>>> in all situations that applications might wish to represent.
>>>>>>>>
>>>>>>>> At heart: when it comes to exchanging provenance information, why
>> do
>>>> we
>>>>>>>> *need* to know exactly what makes one entity a constrained view of
>>>>>>>> another? What breaks (at the level of exchanging provenance
>>>> information) if
>>>>>>>> we have no access to such information? How are applications that
>>>> exchange
>>>>>>>> provenance information about entities for which they don't actually
>>>> know
>>>>>>>> about these attributes to know about their correspondences with
>> real-
>>>> world
>>>>>>>> things?
>>>>>>>>
>>>>>>>> I think the role of attributes here is mainly to *explain* some
>> aspects
>>>> of the
>>>>>>>> provenance model, but they do not need to be part of the model.
>>>>>>>>
>>>>>>>> To my mind, a simpler approach would be to allow for assertion of
>> an
>>>> IVPof
>>>>>>>> type of relationship between entities, from which some useful
>>>> inferences
>>>>>>>> about any attributes present might flow, but I don't see the need for
>>>> the
>>>>>>>> attributes to be in any sense defining of the entities.
>>>>>>>>
>>>>>>>> <aside>
>>>>>>>> My suggested definition of IVPof might be something like this:
>>>>>>>>
>>>>>>>> A IVPof B iff forall p : (Entity ->   Bool) . p(B) =>   p(A)
>>>>>>>>
>>>>>>>> where A, B are Entities, and the values of p are predicates on
>> Entities.
>>>>>>>> </aside>
>>>>>>>>
>>>>>>>> ...
>>>>>>>>
>>>>>>>> #g
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>
>>>
>>>
>
Received on Wednesday, 19 October 2011 15:52:42 GMT

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