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Re: PROV-ISSUE-333 - feedback on PROV-CONSTRAINTS

From: Graham Klyne <graham.klyne@zoo.ox.ac.uk>
Date: Mon, 09 Apr 2012 09:48:45 +0100
Message-ID: <4F82A26D.90505@zoo.ox.ac.uk>
To: public-prov-wg@w3.org
Thinking further about my comments yesterday, it occurs to me that there are two 
additional things that would be helpful to include:

(1) in the introduction, a brief summary of the constraints introduced. 
Offhand, I can think of two:
- variability of an entity must be constrained so that any provenance expressed 
is durable, or immutable.  (E.g. when we say a report was edited by X, the 
report entity referenced must be a version that was and always will be edited by X.)
- timing properties expressed must be consistent with common expectations; e.g. 
that an artifact must be generated before it can be used, etc.
I'm sure there are more, but I'm not sure that reading the document as it stands 
would actually tell me what they are.

(2) some discussion (but no more than that) of how to recast provenance that 
does not conform the the required constraints into a form that does, and which 
can therefore be safely combined with other provenance expressions and have 
inferences drawn.  This discussion would help users of provenance to understand 
that that "scruffy" provenance information can be used in a formal reasoning 
environment if it is subjected to appropriate "conditioning".  For example, if 
Paul says that he is author of his blog post on a given date (but on other dates 
there may be guest posts by other people), then the URI for the blog post can be 
replaced by one that refers to a specific date.  The exact mechanism for this 
would not be specified, but one might point to ideas like Memento, tdb: URI 
scheme or just bog post permalinks.  For timing constraints, one might need to 
say something about re-casting all timestamps in terms of UTC/Zulu-time.  And so on.

#g
--

On 08/04/2012 22:19, Graham Klyne wrote:
> 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
> needs:
> (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.
>
> #g
>
>
Received on Monday, 9 April 2012 08:50:02 GMT

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