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Re: complementOf -> viewOf: proposed text: however... :-)

From: James Cheney <jcheney@inf.ed.ac.uk>
Date: Fri, 13 Jan 2012 13:10:25 +0000
Cc: Graham Klyne <Graham.Klyne@zoo.ox.ac.uk>, Khalid Belhajjame <Khalid.Belhajjame@cs.man.ac.uk>, "public-prov-wg@w3.org" <public-prov-wg@w3.org>
Message-Id: <49B17940-CD43-452D-BA86-97C6FCDA3AFF@inf.ed.ac.uk>
To: Paolo Missier <Paolo.Missier@ncl.ac.uk>
Hi Paolo,

I wondered about this too, and I think it would be sensible for all of the entities that are "about the same thing" to form a lattice, but not the whole set.  (This could just be a partial order without a unique largest element).  The top element of each lattice is "the most general description of the thing".  These lattices should all be disjoint, or else weird things will happen, as you note.

--James

On Jan 13, 2012, at 12:44 PM, Paolo Missier wrote:

> Graham
> 
> glad you agree, however meanwhile I spotted a problem in my own proposal that entities should form a lattice. It doesn't sit well with your axiom, because
> 
> alternateOf(a, b) and
> alternateOf(c, d)
> 
> it follows that a,b,c,d are /all/ alternate of each other (because their def. is now based on specialization, and specialization is transitive, and there is a Top where they all meet).
> 
> But this is too much :-)
> 
> something has to give... let me sit on transitivity of alternate while I fix the rest of the text
> 
> -Paolo
> 
> 
> 
> On 1/12/12 6:32 PM, Graham Klyne wrote:
>> Paolo,
>> 
>> Summary:  I think we are in agreement.  I may need to re-check the text to make
>> sure it doesn't still lead me to one of the misunderstandings from my earlier
>> message.
>> 
>> On 12/01/2012 10:06, Paolo Missier wrote:
>>> Graham
>>> 
>>> sorry for letting this slip. To recall, the context is that I am tasked with
>>> fixing the alternateOf section of PROV-DM.
>>> 
>>> I have a few comments to yours and Khalid's. Original text copied where needed.
>>> 
>>> My main comment is that I like your axiomatization of the two relations, but it
>>> seems to lead to properties that are not exactly what we want. But there is a
>>> simple fix.
>> :)
>> 
>>> Specifically:
>>> 
>>>> In other words, what I am suggesting is that:
>>>> specializationOf(e1,e2) implies alternateOf(e1,e2)
>>> that's fine, I have no problems with that.
>>> 
>>>> *BUT*, this is not what the current text allows, since specializationOf is
>>>> defined to be anti-symmetric, which means that it is also anti-reflexive:
>>>> 
>>>> forall (a, b) : specializationOf(a,b) =>  not specializationOf(b,a)
>>>> 
>>>> setting b = a we see that specializationOf(a,a) must be false, since its truth
>>>> would give rise to a contradiction.
>>> not really. Anti-symmetry is defined differently. I hate to quote wikipedia, as
>>> I don't have the provenance of the content handy :-), but it's just convenient, so:
>>> http://en.wikipedia.org/wiki/Antisymmetric_relation
>>> 
>>> basically, an anti-symmetric relation can be reflexive so that's not a problem.
>> That would be good.  From memory, I wasn't going so much by a definition of
>> "antisymmetry" but because I though the text was suggesting something like the
>> implication above.  But if that's not intended, we can focus on making sure the
>> text doesn't confuse.
>> 
>>> More interestingly, about transitivity of alternateOf(): I believe we can still
>>> save your axiomatization:
>>>> alternativeOf(a, b) == exists (c) :
>>>> specializationOf(a,c) and
>>>> specializationOf(b,c)
>>> just by insisting that the set of all entities forms a lattice. In fact, we only
>>> need an upper semi-lattice.
>> Yes, I think that's about where I'd got to, but I wasn't sure how to axiomatize
>> that cleanly.
>> 
>>> This does not ensure that
>>>> specializationOf(x, y) or specializationOf(y, x)
>>> but it does ensure that for each x,y, there is some z such that
>>> 
>>> specializationOf(x, z) and specializationOf(y, z). alternateOf(a,c) follows.
>>> 
>>> Having a top element is quite natural in class hierarchies (see owl:Thing). But
>>> this should come as no surprise as all we are doing is re-invent class
>>> hierarchies with a a top element.
>>> 
>>> So in summary:
>>> - I am fine with your axiomatization, plus the easy condition that entities form
>>> an upper semi-lattice.
>>> - I think it belongs in PROV-SEM
>>> - I am inclined to keep the properties of the two relations as they are.
>>> 
>>> (and yes, more specific may be better than more concrete).
>>> 
>>> are we in agreement?
>> On the basis of what you say here, yes.
>> 
>> Thanks.
>> 
>> #g
>> --
>> 
>>> On 1/6/12 4:44 PM, Graham Klyne wrote:
>>>> Paolo,
>>>> 
>>>> I've now looked at the text and am happy with the direction, but have some
>>>> niggles with the details...
>>>> 
>>>> First a nit: you say e1 and e2 provide a more *concrete* characterization than
>>>> e1. I would say more *specific* rather than more *concrete*.
>>>> 
>>>> For the rest, using Using Khalid's comments as a spingboard:
>>>> 
>>>> On 05/01/2012 18:43, Khalid Belhajjame wrote:
>>>>> Hi,
>>>>> 
>>>>> The new Alternate and Specialization records seem to make sense to me.
>>>>> 
>>>>> - Looking at the definitions of *specializationOf* and *alternateOf*, I for few
>>>>> seconds was wondering if it is a good idea to define a more general relationship
>>>>> that simply says that two entity records are representations of the same entity,
>>>>> without specifying if there is difference in abstraction or context. But, I
>>>>> changed my mind as a result, and I now think that the general relationship that
>>>>> I was looking for is *alternateOf* itself. Indeed, such a relationship seems to
>>>>> be usable in both cases, i.e., different abstractions and/or different contexts.
>>>>> In other words, what I am suggesting is that:
>>>>> specializationOf(e1,e2) implies alternateOf(e1,e2)
>>>>> 
>>>>> Does that make sense?
>>>>> 
>>>> I think this depends on how the definitions are set up.
>>>> 
>>>> I see specializationOf as a primnitive using which alternativeOf can be defined:
>>>> 
>>>> alternativeOf(a, b) == exists (c) :
>>>> specializationOf(a,c) and
>>>> specializationOf(b,c)
>>>> 
>>>> My preference is for specializationOf to be reflexive; i.e.
>>>> 
>>>> forall (a) : specializationOf(a, a)
>>>> 
>>>> your result follows from this:
>>>> 
>>>> given:
>>>> specializationOf(e1,e2) [per premise]
>>>> specializationOf(e2,e2) [per reflexivity]
>>>> 
>>>> we set a=e1, b=e2, c=e2 to satisfy the RHS of alternativeOf definition, hence
>>>> have alternativeOf(e1, e2) as you suggest.
>>>> 
>>>> 
>>>> *BUT*, this is not what the current text allows, since specializationOf is
>>>> defined to be anti-symmetric, which means that it is also anti-reflexive:
>>>> 
>>>> forall (a, b) : specializationOf(a,b) =>  not specializationOf(b,a)
>>>> 
>>>> setting b = a we see that specializationOf(a,a) must be false, since its truth
>>>> would give rise to a contradiction.
>>>> 
>>>> Which in turn means that the above proof of your suggested inference does not
>>>> hold.
>>>> 
>>>> ...
>>>> 
>>>> So my question is this: is there any particular reason to require anti-symmetry
>>>> of specializationOf?
>>>> 
>>>> (An alternative would be to modify the definition of alternativeOf, thus:
>>>> 
>>>> alternativeOf(a, b) == exists (c) :
>>>> (specializationOf(a,c) or a = c) and
>>>> (specializationOf(b,c) or b = c)
>>>> 
>>>> Absent and particular reason to do otherwise, I'd rather go with the simpler
>>>> definitions.)
>>>> 
>>>> 
>>>>> - *alternateOf* is transitive.
>>>> I think it should be, but let's see how this plays:
>>>> 
>>>> alternativeOf(a, b) == exists (x) :
>>>> specializationOf(a,x) and
>>>> specializationOf(b,x)
>>>> 
>>>> alternativeOf(b, c) == exists (y) :
>>>> specializationOf(b,y) and
>>>> specializationOf(c,y)
>>>> 
>>>> If we can show specializationOf(x, y) or specializationOf(y, x) then the result
>>>> can be derived using transitivity of specializationOf and the definition of
>>>> alternativeOf.
>>>> 
>>>> We have:
>>>> specializationOf(b,x) and
>>>> specializationOf(b,y)
>>>> 
>>>> Intuitively a specializationOf relation holds between x and y as their is a
>>>> single non-branching path from b to the "top" of the specialization tree. But I
>>>> think we need more stated constraints to derive this.
>>>> 
>>>> Right now, I'm not sure how best to capture this, and am thinking that simply
>>>> asserting the required relation would be easiest; i.e.
>>>> 
>>>> specializationOf(b,x) and
>>>> specializationOf(b,y)
>>>> |=
>>>> specializationOf(x,y) or specializationOf(y,x)
>>>> 
>>>> (If specialization is anti-reflexive, we need to add "or x = y" to the above
>>>> constraint.)
>>>> 
>>>> Or maybe:
>>>> 
>>>> specializationOf(b,x) and
>>>> specializationOf(b,y)
>>>> |=
>>>> exists (z) : specializationOf(x,z) and specializationOf(y,z)
>>>> 
>>>> An alternative would be to not care about this, in which case alternativeOf is
>>>> not inferrable from specializationOf. Does this actually matter?
>>>> 
>>>> #g
>>>> --
>>>> 
>>>>> On 15/12/2011 15:25, Paolo Missier wrote:
>>>>>> Hi,
>>>>>> 
>>>>>> in response to the comments about complementarity on the wiki and on the list,
>>>>>> we have prepared a revised version of the section,
>>>>>> where "complementarity" disappears in favour of "viewOf", and the definition
>>>>>> is hopefully simplified and more in line with the
>>>>>> expectations:
>>>>>> http://dvcs.w3.org/hg/prov/raw-file/default/model/ProvenanceModel.html#record-complement-of
>>>>>> 
>>>>>> (the anchor name hasn't changed :-))
>>>>>> 
>>>>>> this is for feedback as per today's agenda
>>>>>> 
>>>>>> atb -Paolo
>>>>>> 
>>>>>> 
>>> 
> 
> 
> -- 
> -----------  ~oo~  --------------
> Paolo Missier - Paolo.Missier@newcastle.ac.uk, pmissier@acm.org
> School of Computing Science, Newcastle University,  UK
> http://www.cs.ncl.ac.uk/people/Paolo.Missier
> 
> 
> 


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Received on Friday, 13 January 2012 13:14:18 UTC

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