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Re: Models and their use

From: Simon Miles <simon.miles@kcl.ac.uk>
Date: Wed, 13 Jul 2011 13:35:40 +0100
Message-ID: <CAKc1nHeQDu0qgoH=uSFNkaQ6OdWX0Ok6RQdqzWTpF=Wi8S6ktg@mail.gmail.com>
To: Provenance Working Group WG <public-prov-wg@w3.org>
Jim, Graham,

Reading through your comments, I'm pretty much in agreement with them.
The discrepancy between my view and Jim's is, I think, just a matter
of what we assume is being defined at the moment (i.e. by
entity/thing).

As in Graham's last mail, I am assuming that we are first defining any
(contextualised) entity ((1) in Graham's classification).

I fully agree with you that assertion/observation/description (2) is
also an important and distinct concept. However, I see it as secondary
to the idea of entity in the model and, as Graham says, a description
is itself a kind of entity. This may be comparable to agents or
process executions, i.e. agents, executions and descriptions are all
particularly important (for provenance) subclasses of entity.

And I think this difference in our views about what was being defined
by "thing" nicely illustrates the original point I was trying to make
about the conflation in the definition :-)

Thanks,
Simon

On 13 July 2011 11:01, Graham Klyne <GK@ninebynine.org> wrote:
> Jim,
>
> I've been thinking about your comments, and have come to a view that there are
> two things going on here, which are not being clearly distinguished:
>
> 1. an entity constrained to some context
>
> 2. observations or descriptions of an entity
>
> which when combined can model observations/descriptions of an entity constrained
> to some context.  I have been focusing on (1), with the expectation that (2)
> would be dealt with separately in the model, where provenance is a kind of
> description.  If I understand correctly, you are particularly concerned to
> distinguish between entity and description.  It seems to me that "bob" has been
> adopted variously to fulfil both these distinctions.
>
> ...
>
> Example: suppose we're interested in Halley's comet, and in particular in the
> periods when it is close to the sun or visible from earth.  So we have two
> concepts:  Halley's comet and Halleys comet when close to Earth.  To my mind,
> these are both *entities* (sensu F2F1).  Any description that is true of
> Halley's comet generally should also be true of it when close to Earth, but
> there are many other assertions are true the constrained Halley's comet that are
> probably not true at all times (e.g. the appearance of a tail due to expulsion
> of gas and dust caused by solar heating).
>
> The page http://en.wikipedia.org/wiki/Halley's_Comet is a *description* of
> Halley's comet.  Being a Wikipedia page, it probably changes over time.  So we
> may wish to discuss it as it exists in a particular period of time.  Today, for
> example, it contains a list of 95 references indicating sources of information
> used in the page.  Thus we may expect this page to be a description of Halley's
> comet for its entire lifetime, but needs to be constrained to make statements
> about the number of references it contains.  In this respect, the page is both
> an "entity" and a "description" of an entity.
>
> The page at http://en.wikipedia.org/wiki/Halley's_Comet also has a brief
> description of a Cuneiform-inscribed clay tablet which is both an entity in its
> own right, with its own description and provenance, *and* a record of
> observation of Halley's comet.  I don't think we can easily disjoin the class of
> descriptions from the class of entities.
>
> Thus, I perceive that the notion of constraint so that some aspects of a
> constrained entity are invariant needs to be dealt with separately from the
> notion of description, which often (but not always, I think) applies to a
> constrained form of some entity.
>
> Does this make any sense?
>
> #g
> --
>
>
> Jim McCusker wrote:
>> My issue is more with Simon's desire to conflate things with the
>> descriptions of those things. We need to be able to say "x, as
>> described by y", which is a separate issue from relating "x1" as an
>> invariant view of "x2".
>>
>> "x as described by y" can be done in semweb using a URI for X and the
>> URI for a named graph or graph literal for y, assuming that there are
>> assertions in y about x. Another alternative is that y can be
>> discussed as an information artifact, as in the Information Artifact
>> Ontology (http://code.google.com/p/information-artifact-ontology).
>> Since x changes over time, we need something that nails down what was
>> actually "seen", or at least, claimed when the agent identified x in
>> its context.
>>
>> A BOB is the y in the above paragraph, and I think that the fact that
>> it's something that's describing an x, it must have the extra
>> qualification in place in its name.
>>
>> Jim
>>
>> On Tue, Jul 12, 2011 at 3:27 PM, Graham Klyne <GK@ninebynine.org> wrote:
>>> [Off-list]
>>>
>>> Jim,
>>>
>>> I had some small reservations about Simon's definition, but I felt that it
>>> was such a big improvement over what we currently have that I didn't want to
>>> muddy the waters just yet by adding qualifications to my support :)
>>>
>>> (Specifically, I would remove "and something more is invariant about B" from
>>> the efinition of invariant view, so that anything can be an invariant view
>>> of itself (or not excluded from so being) - which I think is one of the
>>> concerns you raised.)
>>>
>>> Apart from that, I think there is an aspect of an invariant view that is in
>>> some sense fundamentally subsumptive -- there is a distinct sense that A and
>>> B are generally the same, except that one may be more constrained.
>>>
>>> But, more importantly, I think we need to be looking to say less, not more.
>>> I feel that Simon's definition captures close to what we need to say without
>>> adding too much more.
>>>
>>> In this, I'm arguing for the minimum useful semantics - it's easier to add
>>> (or layer) constraints later than to remove them from an established
>>> defintion.  By providing a little as we can for people to disagree with, I
>>> think we maximize the potential for take-up of the WG outputs.
>>>
>>> #g
>>> --
>>>
>>>
>>> Jim McCusker wrote:
>>>> On Tue, Jul 12, 2011 at 12:02 PM, Graham Klyne <GK@ninebynine.org> wrote:
>>>>> Simon Miles wrote:
>>>>>> To understand the consequences of the above points, I suggest
>>>>>> alternative definitions at the link below:
>>>>>>
>>>>>>
>>>>>> http://www.w3.org/2011/prov/wiki/Talk:F2F1ConceptDefinitions#Entity_and_IVP_of
>>>>> +1
>>>>>
>>>>> I think this is a big improvement over what we have.
>>>> I like the Entity definition, but I'm not sure how we then go about
>>>> qualifying assertions about Entities. We need a way of making those
>>>> assertions (which is what BOBs were for) and a way of relating
>>>> Entities that are the same, even if they aren't mathematically the
>>>> same (different state, different aspect, etc.). IVP of as it's defined
>>>> there is not quite enough, since it only allows for relations between
>>>> entities that have subsumptive (a is IVP of b, therefore a has all the
>>>> states of b plus some).
>>>>
>>>> Jim
>>>> --
>>>> Jim McCusker
>>>> Programmer Analyst
>>>> Krauthammer Lab, Pathology Informatics
>>>> Yale School of Medicine
>>>> james.mccusker@yale.edu | (203) 785-6330
>>>> http://krauthammerlab.med.yale.edu
>>>>
>>>> PhD Student
>>>> Tetherless World Constellation
>>>> Rensselaer Polytechnic Institute
>>>> mccusj@cs.rpi.edu
>>>> http://tw.rpi.edu
>>>>
>>>
>>>
>>
>>
>>
>
>
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-- 
Dr Simon Miles
Lecturer, Department of Informatics
Kings College London, WC2R 2LS, UK
+44 (0)20 7848 1166
Received on Wednesday, 13 July 2011 12:36:10 GMT

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