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RE: Is _this_ what is meant by "Entity"?

From: Myers, Jim <MYERSJ4@rpi.edu>
Date: Sat, 3 Sep 2011 19:06:41 +0000
To: Simon Miles <simon.miles@kcl.ac.uk>, Provenance Working Group WG <public-prov-wg@w3.org>
Message-ID: <3131E7DF4CD2D94287870F5A931EFC23017C80@EX14MB2.win.rpi.edu>
I'm not sure what will make sense to someone who hasn't been through the standardization grinder on this, but I think what you propose might help. I wonder if that could be morphed a bit to talk about the 'OPM'-style case first and then expand. OPM didn't have to deal with entity/thing distinctions because it only considered things that were naturally defined as invariant with repect to the processing that happened.
So - 
entities are PIL constructs representing things in the real world that, in the simplest case, are used and generated by process executions.

To address cases in which process executions merely modify something, PIL provides two mechanisms:

the ability to say an entity participates in a PE - this allows one to record that a PE occurred in the entity's lifecycle but does not allow one to describe the change in the entitiy itself

To describe the change itself, PIL recognizes the possibility to characterize things in the world in different ways and uses this allow provenance records to include entities that characterize things such that changes are viewed as the use of one entity (file-in-location-A) to generate another (file-in-location-B). The definition of entity thus allows one to describe what characterization is intended by identifying fixed attributes that are tied to indentity in that characterization. PIL also includes the ivpOf/complementOf relationship to assert that two entities are characterization of the same thing...

Perhaps better ways to say it, but hopefully the general idea - only introducing the issues of thing/entity and ivpOf/complementOf to talk about mutability after covering the simpler case - comes through.

Cheers,
Jim

________________________________________
From: public-prov-wg-request@w3.org [public-prov-wg-request@w3.org] on behalf of Simon Miles [simon.miles@kcl.ac.uk]
Sent: Saturday, September 03, 2011 2:19 PM
To: Provenance Working Group WG
Subject: Re: Is _this_ what is meant by "Entity"?

Jim,

OK, thanks. I think it's what I thought you meant :-). If we are to
get across clearly and succinctly what you describe, wouldn't it be
preferable to define entity only after process execution and
participation (both in model and primer documents)? Defining
participation requires saying what is participating, which cannot be
entities without definitions being circular, so I would assume
something like:

Defn 1. A thing is anything that can be identified. There are no
assertions directly about things in PIL, but instead about entities
(defined below).

Defn 2. A process execution is an identifiable activity, which
performs a piece of work.

Defn 3. Participation is the involvment of a thing in an activity.

Defn 4. An entity is a view on a thing defined by those
characteristics that do not vary in the process executions it is
asserted to participate in.

["executions it is asserted to participate in" may not be all
processes we want to define an entity relative to, but I can't see
what else is concrete enough to be usable.]

Defn 5. processExecution(id,rl,st,et) is an assertion that a process
execution, identified by id, occurred, and followed recipe rl
(optional) from start time st (optional) to end time et (optional).

Defn 6. entity(id, [ attr: val, ...]) is an assertion that a thing
existed and the entity defined by characteristics [ attr: val, ...],
identified by id, was a view on that thing consistent with the
participations asserted about it.

Defn 7. hasParticipant(pe, e) is an assertion that the thing on which
entity e is a view participated in process execution pe.

Are those definitions adequate to capture everything yet? They may
still be more complicated than is helpful in getting people to adopt
the standard...

Thanks,
Simon
Received on Saturday, 3 September 2011 19:07:10 GMT

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