W3C home > Mailing lists > Public > public-prov-wg@w3.org > July 2011

PROV-ISSUE-60: comments on bob [Conceptual Model]

From: Provenance Working Group Issue Tracker <sysbot+tracker@w3.org>
Date: Fri, 29 Jul 2011 09:06:12 +0000
To: public-prov-wg@w3.org
Message-Id: <E1Qmj1I-00040X-Qg@lowblow.w3.org>

PROV-ISSUE-60: comments on bob [Conceptual Model]

http://www.w3.org/2011/prov/track/issues/60

Raised by: Graham Klyne
On product: Conceptual Model


"A BOB represents an identifiable characterized entity."

What does it mean to be "characterized" here?  What does this tell us?
What does it mean to not be "characterized"?  If this refers to the
attribute-based assertions mentioned earlier, does this mean that if
there are no such assertions, an entity cannot be a "BOB"?

[[ A BOB assertion is about a characterized entity, whose situation in
the world is variant. A BOB assertion is made at a particular point
and is invariant, in the sense that all the attributes are assigned a
value as part of that assertion.  ]]

This section is, according to its heading, about "BOB".  But this is
defining a different concept, so shouldn't this be in a separate
section?

It seems to me that what we're talking about here is a "provenance
assertion". I think it would be clearer to just describe that, e.g.
[[ A provenance assertion is about an entity, whose situation in the
world is generally assumed to be variable.  ]]

I either don't understand or don't agree with the second part of that
description.  The notion of assigning values as party of an assertion
seems wrong to me (I think the notion of constraining attributes is
the job of the IVP-of relation).  I would expect something like:

[[ A provenance assertion is made at a particular point and is
invariant, in the sense that the attributes it mentions do not change
for the entity concerned.  ]]

[[ A BOB assertion must describe a characterized entity over a
continuous time interval in the world (which may collapse into a
single instant). Characterizing an entity over multiple time intervals
requires multiple BOB assertions, each with its own identifier. Some
attributes may retain their values across multiple assertions.  ]]
This constraint seems rather unnecessary, and maybe
counter-productive.

Suppose we want to describe the collective observations of a
particular telescope when pointed at a particular region of the sky.
This might actually consist of a (possibly unknown) number of disjoint
time-segments caused by the rotation of the earth and other factors. I
can't see any clear benefit in being forced to treat these
observation-sets as distinct entities.

[[ There is no assumption that the set of attributes is complete and
that the attributes are independent/orthogonal of each other.  ]] I
don't see this adding any useful information here.  Remove?
Received on Friday, 29 July 2011 09:06:13 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Thursday, 26 April 2012 13:06:37 GMT