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Re: proposed response to public comment (deadline Tuesday noon GMT)

From: Graham Klyne <graham.klyne@zoo.ox.ac.uk>
Date: Tue, 06 Nov 2012 12:32:36 +0000
Message-ID: <50990364.8060504@zoo.ox.ac.uk>
To: Luc Moreau <L.Moreau@ecs.soton.ac.uk>
CC: "www-archive@w3.org" <www-archive@w3.org>, Graham Klyne <graham.klyne@zoo.ox.ac.uk>

I'm responding privately (cc'ed to www-archive), as I said I'd stay out of the 
WG discussion having made a public objection.  I wanted you to be aware that I 
don't feel this response addresses my concerns.  If you choose to do so, you may 
introduce this message into WG discusions, but I feel that has to be your 
decision, not mine.  (You should be able to find the www-archive link somewhere 
in http://lists.w3.org/Archives/Public/www-archive/2012Nov/ if you wish to refer 
to this message.)

The substance of my specific objection is that in its present form, the Mention 
construct is inadequately described, and appears to serve no useful purpose that 
is not already possible, and if left to stand may be used in ways not explicitly 
sanctioned that may be non-interoperable.  Your response here does not affect my 
view on this.

* http://lists.w3.org/Archives/Public/public-prov-comments/2012Aug/0001.html
   (my original objection)
* (others at the end of this message)

Responding to specific points in your proposed response:

On 05/11/2012 07:42, Luc Moreau wrote:
> Dear all, kind reminder.
> Thanks
> Professor Luc Moreau
> Electronics and Computer Science
> University of Southampton
> Southampton SO17 1BJ
> United Kingdom
> On 1 Nov 2012, at 16:33, "Luc Moreau" <l.moreau@ecs.soton.ac.uk<mailto:l.moreau@ecs.soton.ac.uk>> wrote:
> Dear all,
> At http://www.w3.org/2011/prov/wiki/ResponsesToPublicComments#PROV-DM_.28Under_Review.29
> you will find proposed answers to the ISSUE-475. It is copied below for your convenience.
> It will become the group response unless we hear objections by Tuesday November 6th, noon GMT.
> Best regards,
> Luc
> ISSUE-475 (Mention)
>    *   Original email: http://lists.w3.org/Archives/Public/public-prov-comments/2012Aug/0001.html
>    *   Tracker: http://www.w3.org/2011/prov/track/issues/475
>    *   Group Response:
>       *   The reviewer suggests that the work to describe contextualized provenance should be deferred so that it can be aligned with ongoing W3C work on RDF datasets and their semantics. Since ISSUE-475 was submitted, the RDF working group has decided that it will not provide a formal semantics for RDF Datasets. This RDF resolution ensures that any semantics for bundle and/or mention is guaranteed not to be in conflict with the RDF semantics.

If the RDF group can't provide a semantic framework for RDF dataset constructs, 
I don't think the PROV group is qualified to do so.  mentionOf can only be 
expressed in RDF by making reference to RDF dataset or similar constructs.

In the absence of RDF-imposed semantic constraints, we may be free to introduce 
our own contextual semantics for RDF datasets, but at the risk of creating 
inconsistencies with semantics defined by other groups who are similarly free. 
Further, the decision of the RDF group to not define any semantic framework at 
this time does not prevent a future RDF working group from so doing.

(BTW, I'm considering objecting to this lack of provision of a semantic 
framework for RDF datasets by the RDF group.)

>       *   As PROV-Constraints section 6.2 clearly indicates, PROV-bundles validity is determined by examining bundles in isolation of each other. Our response to issue-482 also indicates that PROV itself does not set any constraints on how a given ID is being used across multiple bundles. Given this, mentionOf is a general relation which allows an entity to be linked to another entity described in another bundle.

In which case, unless it is semantically vacuous, this mentionOf construct 
violates this principle of independent validity, since it makes cross-bundle 
references.  Any non-trivial semantic constraints on mentionOf will impose 
cross-bundle constraints on bundle validity.

>       *   The reviewer suggests that
>     mentionOf(infra, supra, b)
> could simply be expressed as
>    specializationOf(infra, supra)
>    entity(infra, [mentionedIn=b])
>    *
>       *   This design was considered and rejected by the Working Group:
>          *   By design, relations between PROV objects are expressed by PROV relations (usage, generation, etc, mention), and are not expressed as PROV attributes. The suggested additional attribute mentionedIn would relate the entity infra with bundle b, and would go against this prov-dm design.

This design was offered as an example, not a proposal, so I don't think the 
group's rejection of that specific design invalidates my point that the function 
of "mentionOf" can be covered by existing features of the model.  (I would argue 
that, even if the group have not adopted this design, it remains a legal 
construct within PROV-DM modulo choosing a name for "mentionedIn" that is not in 
the prov: namespace.)

>          *   The interpretation of the attribute-value pair mentionedIn=b is somewhat difficult, because infra is not itself described in bundle b: supra is the entity described in bundle b. So, syntactically, mentionedIn=b may look like an attribute-value pair, but in reality, it can only be understood in the presence of specializationOf(infra, supra). Hence, the reason for introducing the ternary relation mentionOf.

Then I misunderstood or misread the specification.  I should have suggested:

   entity(supra, [mentionedIn=b])

With that change the rest of my comment stands.

My comment about redundancy would similarly apply if there were a binary 
mentionedIn relation, but that would require a different new construct in 
PROV-DM, which might appear thus:

     specializationOf(infra, supra)
     mentionedIn(supra, b)

If this form of mentioned had been specified, I would not be objecting.

>       *   The Working Group left it unspecified which new attributes could be inferred for infra, and in general what constraints apply to mentionOf. The reviewer is critical of this decision, arguing that nothing new can be inferred from mentionOf, and therefore mentionOf can be replaced by specializationOf. 'Under-specification' is a feature of PROV: what can be inferred from relations such as usage, derivation, alternate? The group recently acknowledged this for alternateOf and added a clarifiying note in the text. This observation is applicable to further PROV concepts, such as Quotation, PrimarySource, SoftwareAgent, etc. which do not allow us to infer more than their parent concept would (Derivation, Agent). We are in a same situation with mentionOf. Further inferences are left to be specified by applications.

I think the definition of "mentionOf" is the worst kind of underspecification, 
not really comparable with the others you mention (except maybe "alternateOf"). 
  A significant new structure is introduced into the model with no indication of 
its semantics?  This is almost guaranteed to lead to interoperability failure. 
As I've argued elsewhere, I actually think too many constructs have been 
introduced into PROV, but I think that for they most part they are mostly 
harmless, creating "noise" but not likely to lead to fundamental 
interoperability problems.

It would be better in my view to leave implementers to implement their own new 
constructs, with semantics as needed by their applications.  Later, when we see 
what is actually needed, it may be appropriate to select one or some and bless 
them with standard status and semantics.

>       *   The reviewer's suggestion to address the use of Example 45 is to copy part of the referred bundle. By copying statements from the original context to the new context, we have lost the original context in which they occur (... their provenance!), and we have no way of expressing that wasAssociatedWith(ex:a1, ...) in the new context is a "kind of specialization" of wasAssociatedWith(ex:a1,...) in the original context, ... which is why mentionOf was introduced in the first place.

It was my understanding, and I think it's what the specification says, that a 
bundle is simple a collection of provenance statements, *not* a context.

"A bundle ◊ is a named set of provenance descriptions, and is itself an entity, 
so allowing provenance of provenance to be expressed."

In particular:  the provenance of a bundle *has no effect on* the semantics of 
the content of the bundle.  Thus, COPYING a provenance statement from one bundle 
to another has no effect on the claim it makes.  (The provenance of a bundle 
within which it appears may affect one's decision to trust that statement, but 
that's a different issue that lies beyond the scope of PROV as defined.)

>       *   The reviewer also comments on the lack of information about 'Fixed aspects'. We refer to our response to ISSUE-462, and recent associated changes to the document.

I don't believe this adds any useful information with respect to my present 
objection.  Indeed, this aligns with the interpretation I *assumed* when framing 
my objection.

>       *   The Working Group identified 'mention' as a feature at risk, because it was seeking experience from implementers. The Working Group will keep this feature marked at risk as it enters the CR phase, and will reassess its suitability based on implementers feedback.

My position as a member of the working group was, and is, that this is a feature 
that needs to be more widely *reviewed* - maybe that didn't find itself into the 
wording of the "at risk" notation.

I note the wording used is:
This feature is "at risk" and may be removed from this specification based on 
feedback. Please send feedback to public-prov-comments@w3.org.

The "Mention" construct might be removed from PROV if implementation experience 
reveals problems with supporting this construct.
-- http://www.w3.org/TR/2012/WD-prov-dm-20120724/#term-mention

Since the second statement does not exclude the first (which says nothing about 
*implementation*), I disagree with your narrower interpretation of "at risk".


>    *   References:
>       *   RDF resolution: http://www.w3.org/2011/rdf-wg/meeting/2012-10-03#resolution_1
>       *   Email discussion on mention: http://lists.w3.org/Archives/Public/public-prov-wg/2012Jun/0400.html
>       *   alternateOf: http://dvcs.w3.org/hg/prov/diff/60b6ee097555/model/prov-dm.html#l1.8
>       *   Response to ISSUE-482: http://www.w3.org/2011/prov/wiki/ResponsesToPublicComments#ISSUE-482_.28Bundles_and_IDs.29
>       *   Prov constraints section 6.2: http://www.w3.org/TR/prov-constraints/#bundle-constraints
>       *   Response to ISSUE-462: http://www.w3.org/2011/prov/wiki/ResponsesToPublicComments#ISSUE-462_.28Definition_of_Entity.29
>    *   Changes to the document:
>    *   Original author's acknowledgement:
> [edit<http://www.w3.org/2011/prov/wiki/index.php?title=ResponsesToPublicComments&action=edit&section=46>]
> --
> 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<mailto:l.moreau@ecs.soton.ac.uk>
> United Kingdom                     http://www.ecs.soton.ac.uk/~lavm
Received on Tuesday, 6 November 2012 12:34:05 UTC

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