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Re: Dictionary/Collection: where are we?

From: Luc Moreau <L.Moreau@ecs.soton.ac.uk>
Date: Thu, 07 Jun 2012 10:15:22 +0100
Message-ID: <EMEW3|5562b13d1f09200df088e75ade33115bo56AFO08L.Moreau|ecs.soton.ac.uk|4FD0712A.2080202@ecs.soton.ac.uk>
To: public-prov-wg@w3.org
Thanks for adding this point, Paolo.

Luc

On 06/07/2012 10:06 AM, Paolo Missier wrote:
> Luc,
>
> this is a good summary and as I have stated in the past, I see no 
> problems with 1-10.
> My understanding of the OWA/CWA issue is that it only comes into play 
> when one tries to incorporate _new_ knowledge into an existing set of 
> provenance statements, which affects collections because they are the 
> only costruct that carries state (so your new statements mau change 
> your knowledge of what you knew about was the state). But because of 
> (7) and (8) below, this reduces to whether one can have multiple 
> insertions/removal assertions about the same collection, but this is 
> already forbidden: 
> http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-constraints.html#collection-unique-derivation 
>
>
> So I would just go with option 1 below
>
> -Paolo
>
>
>
>
> On 6/7/12 8:59 AM, Luc Moreau wrote:
>> Dear all,
>>
>> We have had multiple threads discussing collections lately.
>> I would like to summarise what collections currently are in prov-dm, 
>> and check whether it's still what people want.
>>
>> 1. A notion of EmptyDictionary:  it's complete knowledge, no future 
>> knowledge can change its empty nature
>>
>> 2. A relation insertion that completely list pairs to be added to a  
>> dictionary, with an update semantics.
>>
>> 3 A relation removal that completely lists keys of pairs to be 
>> removed from the dictionary
>>
>> 4. The property that the state of a dictionary is computable: given a 
>> complete knowledge of a dictionary, any sequence of insertion/removal 
>> leads to a dictionary whose state can exactly be computed.
>>
>> 5. Incomplete knowledge of a dictionary state can be modelled  by not 
>> specifying the initial state of a dictionary (see d1,d2 in example 
>> http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-dm.html#example_53) 
>> or by introducing derivations (see c2 in example 
>> http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-constraints.html#collections-and-derivation) 
>>
>>
>> 6 so far, no mention of membership relation!
>>   So, if there are issues regarding CWA, they need to be discussed 
>> for the above.
>>
>> 7. Membership defined, in this context, as a convenience notation for 
>> an insertion operation into an unspecified dictionary.
>> See  constraint 38 in prov-constraints 
>> (http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-constraints.html#membership-as-insertion). 
>>
>>
>> 8. Complete membership defined, in this context, as a convenience 
>> notation for an insertion operation into an empty dictionary.
>>
>> 9. There was a request to disallow complete membership. Given that 
>> this is just a convenience notation, it's unclear why we do this? 1, 
>> 2, 3, 4 are all about complete knowledge of a dictionary state.
>>
>> 10. Prov-dm define a type prov:collection but NO relation that 
>> applies to it.
>>
>> 11 a further point was discussed: can we specify a membership 
>> relation for collections. given point 4 above, the axiomatisation of 
>> dictionary requires comparison of its members. It's ok for 
>> dictionaries, since we compare keys. It's unclear how we can make 
>> this compatible with a membership for a collection of entities.
>>
>> Where does it leave us?
>>
>> 1. Do we want to allow dictionaries for which we have complete 
>> knowledge of the contents?
>> 1.1 if yes, what's the point of removing the complete flag
>> 1.2 if no, .... Go back to drawing board for dictionaries ....
>>      ... Realistically, that looks like the final nail ...
>>
>> 2. If we have specified dictionaries and their relations, then do we 
>> need to specify some relations for collections?
>>
>
>

-- 
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
United Kingdom                     http://www.ecs.soton.ac.uk/~lavm
Received on Thursday, 7 June 2012 09:15:58 UTC

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