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RE: PROV-ISSUE-85 (What-is-Entity): Definition of Entity is confusing, maybe over-complex [Conceptual Model]

From: Myers, Jim <MYERSJ4@rpi.edu>
Date: Tue, 6 Sep 2011 14:51:28 +0000
To: Luc Moreau <L.Moreau@ecs.soton.ac.uk>, "public-prov-wg@w3.org" <public-prov-wg@w3.org>
Message-ID: <3131E7DF4CD2D94287870F5A931EFC230182F3@EX14MB2.win.rpi.edu>
First - thanks for persevering!

I don't think we can separate characterized thing and situation in the world the way you'd like - if we change the situation - i.e. the parts we want to fix, we actually change the characterization.  As in my email a few minutes ago to Graham, if we consider a 'file' to be mutable w.r.t. name/path/location, it isn't really a file any more - it's some 'logical file' (Reagan Moore used this term for SRB/iRODS). I think this is generally true though we often colloquially use the same term (like file) for multiple characterizations, we can't actually come up with a consistent definition if we do that (I think Allen Renear's argument that mutable documents can't exist is essentially this).

What that does to a definition is to make the attributes directly about how you're characterizing the thing. The ID represents a thing as characterized by the fixed attributes provided. 'Luc in Boston' is a thing (no offense :-) characterized by a name and location and perhaps by a 'base type' of person since we expect Luc-in-Boston to behave like a person (Be mutable in the ways a person is even though Luc-in-Boston does not fit fully fit the definition of person since people can travel between cities). (Graham - perhaps this is the better way to address the file case as well - the logical file has a base type of file rather than inventing the type logical file or document version for it).

The way the situation in the world comes in is really that some characterizations are more useful than others when talking about specific situations  - Luc-in-Boston and Luc-in-New-York make it easy to talk about travel.

The issue of uniqueness over several intervals might best be explained by saying that provenance is part of the characterization of a thing and hence Luc-in-Boston who arrived on flight A is different than Luc-in-Boston who arrived on flight B because the provenance is part of the characterization and that is clearly different in these two cases. This has the nice corollary that an entity cannot be created by two different processes (ignoring for now the question of whether there might be more than one way to assert that in PIL - different levels of granularity, etc.) - it is by definition.


> -----Original Message-----
> From: public-prov-wg-request@w3.org [mailto:public-prov-wg-
> request@w3.org] On Behalf Of Luc Moreau
> Sent: Monday, September 05, 2011 10:54 AM
> To: public-prov-wg@w3.org
> Subject: Re: PROV-ISSUE-85 (What-is-Entity): Definition of Entity is confusing,
> maybe over-complex [Conceptual Model]
> Hi Graham, Jim, and Simon,
> Following the discussion this WE, Paolo and I have revised  the definition of
> entity.
> Before editing the document, we would like to get your feedback.
> General assumption (to appear in section 4):  in the real world, we find:
>     - identifiable characterized things, their situation in the world
>     - activities
>     - events
> Cheers,
> Luc
> -----
> Revised section 5.1
> -------
> In PIDM, an entity construct is a representation of an identifiable
> characterized thing.
> An instance of an entity construct, expressed as entity(id, [ attr:
> val, ...]) in the Provenance Abstract Syntax Notation:
> - contains an identifier id, denoting a characterized thing
> - contains a set of attribute-value pairs [ attr: val, ...], representing
>    this characterized thing's situation in the world.
> The assertion of an instance of an entity construct , entity(id, [ attr:
> val, ...]), 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 (which may collapse into a single instant).
> Example: <same example>
> ... states the existence of a thing of type File and location /shared/crime.txt,
> and creator alice, denoted by identifier e0, during some characterization
> interval.
> Further properties:
> - If an asserter wishes to characterize a thing with same attribute-value pairs
> over several intervals, then they are required to assert multiple entity
> assertions, each with its own identifier.
> - There is no assumption that the set of attributes is complete and that the
> attributes are independent/orthogonal of each other.
> Cheers,
> Luc
> On 09/01/2011 05:32 PM, Provenance Working Group Issue Tracker wrote:
> > PROV-ISSUE-85 (What-is-Entity): Definition of Entity is confusing,
> > maybe over-complex [Conceptual Model]
> >
> > http://www.w3.org/2011/prov/track/issues/85

> >
> > Raised by: Graham Klyne
> > On product: Conceptual Model
> >
> > See also:
> > http://lists.w3.org/Archives/Public/public-prov-wg/2011Aug/0383.html

> >
> > Section 5.1.
> >
> > The definition of "Entity" seems to introduce un-needed complications.  I
> don't see anything here that fundamentally distinguishes an entity from
> anything that can be named, i.e. a web resource.
> >
> > I don't see what useful purpose is served by the insistence on
> "characterized thing".
> >
> > This section seems to spend more effort describing "entity assertion" is is
> apparently a different concept, but not formally part of the model.  There is
> some sense that an entity must have associated entity assertions... but I
> can't see why this is needed, and indeed it may be not possible to enforce
> this idea in RDF's open world model.
> >
> > There's been talk of Entities being part of the occurrent vs continuant
> distinction, but I'm not seeing that explained.
> >
> > Suggest:  why not just have an entity as an identifiable thing, and build the
> rest around that?  What would break with this approach?
> >
> >
> >
> >
> --
> Professor Luc Moreau
> Electronics and Computer Science   tel:   +44 23 8059 4487
> University of Southampton          fax:   +44 23 8059 2865
> Southampton SO17 1BJ               email: l.moreau@ecs.soton.ac.uk
> United Kingdom                     http://www.ecs.soton.ac.uk/~lavm


Received on Tuesday, 6 September 2011 14:54:11 UTC

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