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Re: Collections in PROV-O

From: Graham Klyne <GK@ninebynine.org>
Date: Fri, 24 Feb 2012 14:12:57 +0000
Message-ID: <4F479AE9.2060208@ninebynine.org>
To: Stian Soiland-Reyes <soiland-reyes@cs.manchester.ac.uk>
CC: Paolo Missier <Paolo.Missier@ncl.ac.uk>, Jun Zhao <jun.zhao@zoo.ox.ac.uk>, "public-prov-wg@w3.org" <public-prov-wg@w3.org>
On 24/02/2012 09:56, Stian Soiland-Reyes wrote:
> On Thu, Feb 23, 2012 at 15:59, Paolo Missier<Paolo.Missier@ncl.ac.uk>  wrote:
>> But Stian's rendering is not valid exactly because he is ab-using the
>> insertion mechanism by omitting the key. To me this is "scruffy". I could do
>
> Yes, this is very scruffy. It is like saying X was generated by an
> activity which used Y, but without identifying the activity. That's a
> 'power' of RDF if you like, which would not be easily be mapped to
> PROV-DM (unless we introduce an anonymous _ prefix, like in Turtle)

Or just introduce a new, unique name - like Skolemization?

#g
--

>> Either we introduce an extra relation for containment (and think through how
>> it plays out with the current state update framework), or we use the current
>> framework "properly".  The framework states that the only way you can
>> /achieve/ containment of A into B is by asserting that A was added to B.
>> Containment is a consequence of this.
>
> But Jun might not know when A was added to B, she just observed that B
> (that perhaps came out of a workflow activity) contained A - and
> perhaps later she used A - and so we want to have a trace to say where
> A came from. You can just say that A was derived from B (through a
> get-from-collection kind of activity) - but that's not very
> transparent.
>
> I can see two problems with allowing asserting of collection members:
>
> a) Users could say "impossible" things such as:
>    A contained { (a,1), (b,2) }
>    B was made by adding (c,3) to A
>    B contained { (b,2), (d,4) }.
>
> b) In an open world assumption it might be hard to assert that the
> members of A was x,y,z and nothing else. Other times one might
> actually want to say it contained x,y,z AND possibly something else
> (unknown). See RDF collections and the problem of 'closing' a list.
> [2]
>
>
> We should make collection member containment an issue/request.
>
> Jun - could you write it as an issue in the tracker and give a simple
> usecase for when one would want to state containment?
>
>
>
>> BTW 1: I don't see why having literal keys is a problem. I may be missing
>> it. Nesting is accommodated by having values which are Entities (of type
>> prov:Collection).
>
> How would you represent this set of set of empty sets (ugh!) using literal keys?
>
> A = {
>    { {}, {} }
>    { {} }
>    { }
> }
>
> You have to make up some keys. (I did the inner set members be empty
> sets instead of literals {a,b,c} so you can't be tempted to say "We'll
> call the first key "a_b_c" etc :) )
>
> Two asserters of provenance about modifications to this set could
> generate totally different keys.
>
> If you use entities as keys, it's easy, as you just use the value as
> the key. For bags (unordered, allows duplicates) you still have a
> problem, and would probably have to resort to fresh random-id-assigned
> entity for every key. RDF containers [1] uses rdf:_n for this purpose,
> for instance
>    :bag rdf:_5 :fifth .
> (even if the bag is unordered)
>
>
>> BTW 2: when did prov:Container start to be used for collections?
>
> Sorry, I obviously meant prov:Collection :)
>
> [1] http://www.w3.org/TR/rdf-primer/#containers
> [2] http://www.w3.org/TR/rdf-primer/#collections
>
>
Received on Friday, 24 February 2012 14:15:43 GMT

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