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Dictionary/Collection: where are we?

From: Luc Moreau <L.Moreau@ecs.soton.ac.uk>
Date: Thu, 07 Jun 2012 08:59:10 +0100
Message-ID: <EMEW3|4af719404e66c6f5111cd3dbae9978abo568xD08L.Moreau|ecs.soton.ac.uk|4FD05F4E.90906@ecs.soton.ac.uk>
To: Provenance Working Group WG <public-prov-wg@w3.org>
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 07:59:47 GMT

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