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From: Graham Klyne <graham.klyne@zoo.ox.ac.uk>
Date: Sun, 08 Apr 2012 22:19:30 +0100
Message-ID: <4F8200E2.2000401@zoo.ox.ac.uk>
To: W3C provenance WG <public-prov-wg@w3.org>
Summary:  not ready for release.  Sorry!

I've read this document up to section 2.2 and, based on what I've read, I'm not 
sure I can see any reason for this document to exist.

When we set out on this path of separating the description of constrained (or 
"strict") provenance from "scruffy" provenance, my understanding was that:
(1) we wished to provide an easy-to-understand provenance data model that anyone 
could use to generate and present provenance information, and
(2) we wished to describe a strict, or constrained, use of this model that would 
allow certain conclusions to be validly inferred.

As such, the PROV-CONSTRAINTS document needs to build upon the PROV-DM document 
in a way that doesn't seek to invalidate things that people do based on PROV-DM 
alone (cf. Paul's use-case about making provenance statements about his blog).

Yet this is not what I see when I read the PROV-CONSTRAINTS document.  What I 
see is a document that (a) simply repeats a lot of material that is present in 
PROV-DM (I think familiarity with the contents of PROV-DM should be assumed for 
readers of PROV-CONSTRAINTS), and (b) introduces new definitions that seem to 
invalidate some usage that would be valid based on a reading of PROV-DM alone 
(e.g. the MUST constraint in section 2.1.2, para 3).  I think it is important 
that PROV-CONSTRAINTS MUST NOT invalidate a naive use of the provenance model. 
In this light, I find several parts of the text I have read to be contradictory 
(e.g. section 2.1 paras 3 & 4, or the notion that "event" underpins PROV-DM when 
it isn't even mentioned there).

The goal, as I understand it, is that when provenance statements are made in a 
way that conform to the stricter usage, then certain inferences become valid.

In writing this, I realize that there is something that, to my knowledge, has 
not been discussed in the WG.  If presented with some arbitrary provenance 
information, how is an agent to know if it has been constructed with regard to 
the strict constraints of PROV-CONSTRAINTS, or is simply a looser use of the 
basic provenance model?  Without some way to answer this, I think the "scruffy" 
and "strict" (for want of more evocative terms) approaches to expressing 
provenance are destined to flounder.

So, for this document to work as I understand it is intended to do, I think it 
(1) to start out with a much clearer articulation of its goal - I find the 
present section 1 introduction tells me nothing that I actually need to know 
about the role of PROV-CONSTRAINTS, and
(2) we need a way to recognize when provenance statements are intended to be 
interpreted according to the strict usage defined by PROV-CONSTRAINTS.

For (1), stripping out the introductory references and repetition of PROV-DM, I 
think something like this is needed:

This specification defines a strict, or constrained, usage of the provenance 
data model which, if followed, makes a number of conclusions commonly drawn from 
provenance information to be logically valid inferences.  It also defines a way 
to assert that the provenance usage conforms to this strict usage.  These 
constraints are also reflected in the provenance formal semantics [@@ref].

For (2), I don't have any definite proposal, though I can imagine some 
approaches.  The following are intended as seeds of ideas, not definite suggestions:
* a subproperty of prov:hasProvenance, e.g. prov:hasStrictProvenance, that 
relates provenance to some entity.
* a property associated with a prov:Account that indicates that the provenance 
statements in that account can be interpreted as strict provenance
* a property of an agent or activity associated with generation a provenance 
account that indicates that the generation process follows strict provenance 
constraints in generating provenance statements.
* etc.

Until these fundamental issues are addressed, I think that any further comment 
on the content of this document would be in the league of shuffling deckchairs 
on the Titanic.

Received on Sunday, 8 April 2012 21:21:24 UTC

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