Re: PROV-ISSUE-29 (mutual-iVP-of): can two bobs be mutually "IVP of" each other [Conceptual Model]

Hi Luc,

The point of having each Entity mapped to a (unique) Thing in the semantics is to avoid this kind of confusion.  

I did it this way precisely because of examples like this, and because of I thought there was a rough consensus that specialization 

If you think the formal semantics as is mismatches the data model/constraints and should not do this, please raise an issue on it and we can discuss it.

Considering your (brief) example (I think I am restating Stian's response in more formal terms):

So there are two things:

thing1 = woman in red
thing2 = man in black

I'll assume their lifetimes both include t1,t2.  From t0 to t1, thing1 is in the chair, then thing1 leaves and thing2 gets in the chair at t2.

If you have one "entity"

ent0 = person on chair at times [t1,t2]

then there can't be a single thing that the entity maps to, i.e., it's not allowed in the semantics.

You need two entities 

ent1 = person on chair at time t1
ent2 = person on chair at time t2

Note that officially, we are not required to give ent1 and ent2 different attributes (or any attributes at all), but if we intend them to denote different things

Incidentally, the example you gave has nothing at all to do with specialization: specialization is a relation on entities, not things, and the two entities ent1 and ent2 are not specializations of each other, nor is ent1 or ent2 a specialization of ent0 (or vice versa).  Ent0 is not even a sensible entity anyway.  So, in my view your example is not a use case for allowing entities to refer to multiple things.

I see absolutely no point to or motivation for allowing an entity to refer to more than (or less than) one thing.  

--James

On Apr 1, 2012, at 8:20 PM, Luc Moreau wrote:

> 
> 
> 
> On 1 Apr 2012, at 12:12, "Paul Groth" <p.t.groth@vu.nl> wrote:
> 
>> My answers:
>> 
>> 1. An entity refers to one thing that thing may or may not be identified
> 
> 
> At a given point in time, possibly, but is it the case when time changes?
> 
> Can't recall the exact detail, but the 'customer on the third chair' may be the
> woman in red at t1 and the man in black at t2. Can't it?
> 
> 
> Luc
> 
> 
>> 
>> 2. Specialization thus is defined in terms of 1
>> 
>> Paul - not a specialization/alternator guru 
>> 
>> On Apr 1, 2012, at 9:46, Luc Moreau <l.moreau@ecs.soton.ac.uk> wrote:
>> 
>>> Hi all specializationOf/alternateOf gurus,
>>> 
>>> The current definition of alternateOf does not allow us to decide whether James's or my interpretation
>>> is right.  The question is essentially: does an entity refer to one and only one thing or not.
>>> 
>>> So, 
>>> 
>>> 1. What is intended?
>>> 2. How do we clarify definitions?
>>> 
>>> Cheers,
>>> Luc
>>> 
>>> 
>>> On 31/03/2012 15:46, James Cheney wrote:
>>>> 
>>>> On 30/03/12 10:01, Luc Moreau wrote:
>>>>> 
>>>>> 
>>>>> Dear all,
>>>>> 
>>>>> I am getting conflicting messages on this topic!
>>>>> 
>>>>> James has listed some properties derived from the semantics
>>>>> http://lists.w3.org/Archives/Public/public-prov-wg/2012Mar/0470.html
>>>>> But not all of them seem to be aligned with what we are reading on this thread.
>>>>> 
>>>>> So, I started drafting a section in prov-dm part II listing the properties of these relations [1].
>>>>> 
>>>>> I am proposing to justify each property either by reasoning based on its definition,
>>>>> or by a counter-example.
>>>>> 
>>>>> Your suggestions are needed to help us complete this section.  
>>>>> 
>>>>> James, unless my reasoning is incorrect, I do not have transitivity for specializationOf.
>>>> 
>>>> Hi Luc,
>>>> 
>>>> Your reasoning (quoting from [1])  is:
>>>> 
>>>>> Specialization is not transitive. Indeed if specializationOf(e1,e2) holds, then there is some common thing, say e1-2 they both refer to. Likewise, if specializationOf(e2,e3) holds, then there is some common thing, say e2-3 they both refer to. It does not follow there is a common thing both e1 and e3 refer to.
>>>> 
>>>> In the WD3 formal semantics [2], I modeled entities-referring-to-things as a function thingOf : Entity -> Thing.  
>>>> 
>>>> Thus, if thingOf(e1) = e1-2 = thingOf(e2) and thingOf(e2) = e2-3 = thingOf(e3) then (by transitivity of equality) e1-2 = e2-3 and all three entities refer to the same thing, e1-2.
>>>> 
>>>> Of course, it is an assumption I made that an entity "refers to" exactly one thing.  If we want to allow entities to refer to multiple things, then the reasoning I give above fails, and specializationOf is not necessarily transitive.
>>>> 
>>>> --James
>>>> 
>>>> [1] http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-dm-constraints.html#component4
>>>> [2] http://www.w3.org/2011/prov/wiki/FormalSemanticsWD3
>>>> 
>>>> The University of Edinburgh is a charitable body, registered in
>>>> Scotland, with registration number SC005336.
>>>>