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Re: PROV-ISSUE-183 (prov-dm-identifiers): identifiers in prov-dm [prov-dm]

From: Luc Moreau <L.Moreau@ecs.soton.ac.uk>
Date: Wed, 21 Dec 2011 21:08:33 +0000
Message-ID: <EMEW3|bf23e3eb5a59c3e47401c56da69e99acnBKL8g08L.Moreau|ecs.soton.ac.uk|4EF24AD1.6050906@ecs.soton.ac.uk>
To: public-prov-wg@w3.org
Dear all,

Paolo and I had a discussion about identifiers, and felt that some of 
the terminology
we used was confusing.  Hence we have made some changes, which we 
summarize here.

1.  The identifier that occurs in an entity record is
     the identifier of an entity   ... and not the identifier of the record

2. An account allows for three things:
         - associating asserter with assertions
         - scoping some structural constraints (new section 7.2)
         - scoping for the uniqueness of identifiers

3. Constraint:
http://dvcs.w3.org/hg/prov/raw-file/default/model/ProvenanceModel.html#identifiable-record-in-account
  requires that for a given entity identifier there is a most one entity 
record containing this identifier.



We believe that with the following:
- entity identifiers can be URIs with the usual semantic web understanding
- entity identifiers do *not* double up as URI for entity records
- with the above constraint, given an account and an entity URI, we can 
find an entity record for
      this entity.

We hope these changes will help resolve the debate on identifiers/accounts.
No doubt that we will  discuss that at the teleconference tomorrow.

Luc


On 06/12/11 15:47, Provenance Working Group Issue Tracker wrote:
> PROV-ISSUE-183 (prov-dm-identifiers): identifiers in prov-dm [prov-dm]
>
> http://www.w3.org/2011/prov/track/issues/183
>
> Raised by: Luc Moreau
> On product: prov-dm
>
>
> Hi,
>
> It think that it is now time to have a proper debate about identifiers in prov-dm since comments are regularly expressed about them. I have raised this issue about this topic so that we can track the conversation properly. Our hope is to reach consensus on this topic by the time of the third working draft.
>
> First, in the fpwd, there was a mention of "qualified identifier" (appearing in a note see [1]).  We have removed this term from the second working draft.
>
> Second, the complementarity record now explicitly allows for linking entity records across accounts. Its syntax allows for two accounts to be named.
>
> Third, identifiers for entities in prov-dm have a dual role [3]. An entity has got an id (typically given by an application). An entity record --- i.e. what we say about an entity in a provenance record --- also has an id. There is a consensus that we shouldn't mint identifiers for provenance records. Hence, the identifier of the entity record is defined to be the same as the identifier of the entity.
>
> The consequence of this is that two entity records in different accounts may have the same identifier: they may say different things about the same entity.  For example, the document ex:doc was generated by latex in account1, while in account 2, ex:doc is described to be the result of a survey of a field by different authors.
>
> This explains why we needed the complementarity record to name the accounts as well. This assumes that account names need to be named uniquely (see [4]).
>
> So, entity records identifiers are scoped to accounts.  Note, I said entity *records*, not entities. Hence, we are not breaking the semantic web approach: an entity is a resource and is denoted by a URI, and this remains true in all accounts. (I guess that from a semantic web perspective we are not looking at a provenance record as resource, since we don't have a global URI to name it.) Finally, we allow for accounts to be nested hierarchically; this fits nicely with abstraction in provenance records. Again, see [4].
>
> Can you express your views about this approach, as currently defined in the second draft of prov-dm?
>
> Thanks,
> Luc
>
> [1] http://www.w3.org/TR/2011/WD-prov-dm-20111018/#expression-identifier
> [2] http://dvcs.w3.org/hg/prov/raw-file/default/model/ProvenanceModel.html#record-complement-of
> [3] http://dvcs.w3.org/hg/prov/raw-file/default/model/ProvenanceModel.html#record-Entity
> [4] http://dvcs.w3.org/hg/prov/raw-file/default/model/ProvenanceModel.html#record-Account
>
>
>
>    
Received on Wednesday, 21 December 2011 21:09:06 UTC

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