[topicmapmail] PSIs - alternatives

[Simon Grant]

At 10:25 2006-06-28, Bernard Vatant wrote:
>Steve Pepper:
>>
>>My main point is that we should be extremely careful about keeping agreement
>>concerning the *identity* of a subject separate from agreement concerning
>>*opinions* about a subject. We should therefore avoid overloading the PRD
>>with assertions, especially machine-processable assertions.
>>
>Could you explain how you think that asserting the *identity* of a 
>subject can be cleanly separated from asserting *opinions* about it?

Maybe it is possible to separate it, even if it is not as clean as 
one would like. More below...

>First, asserting that a subject exists as a distinct entity with 
>id-entity is by itself an *opinion*. A subject comes to existence 
>when someone starts to declare something about it, the first 
>declaration being : "Here is something distinct from everything 
>else". This is the expression of an opinion, with which one may agree or not.

Sure, but if one party doesn't agree with the existence of something, 
they won't have a PSI for it, and therefore that subject will not 
have to be merged in any dealings with that party. Hence the 
"opinion" about the existence of something has different qualities 
for our purposes from other kinds of opinion. (I don't mean 
"existence" in a physical sense, but in a conceptual sense.)

>The second step is : "This subject will be identified in such and 
>such a way, enabling to make it distinct from any other subject". 
>Note that, as Patrick has pointed correctly, identification will 
>generally occur in a certain context (domain context, or processing 
>context), so this context is implicitly or explicitly part of the 
>identity declaration, and its definition is also an opinion ... and so on ...
>So, even if I agree on the principle, I don't think this separation 
>can be as neat as you wish it to be (as Lars Marius would say : "The 
>real world is broken"), so there is no point in trying to specify 
>what the limits are, as Simon tried to suggest, or as we tried to do 
>(without success) in the OASIS TC.

Perhaps I ought to look this up. Does anyone have useful references? 
We could always check if any new approaches could be seen.

>Seems to me that a pragmatic approach can rely on the following principles :
>    * Whatever people strongly agree upon belongs to identity side, 
> IOW identity is the "minimal common opinion about the subject".
>    * Whatever people are likely to disagree upon belongs to the 
> assertions/opinions side.

That's a very appealing position. However, I'm not sure that it takes 
into account the fallibility of information and knowledge systems.

Say that we all agreed that date of birth was a good attribute 
amongst a set for identifying people. The problem comes that if, say, 
one party has my date of birth as 1956-03-04 and another 1956-04-03 
by mistake (neither is my actual one!), they might be led erroneously 
to conclude that I was two different people. Thus, one could argue, 
personal identity doesn't *necessarily* include date of birth - 
indeed it doesn't *necessarily* include anything: I could spell my 
name wrongly; I could have a signature or a photo that is easily 
confusable with that of someone else. Etc. etc.

What I'm suggesting is that, firstly, there is no set of attributes 
which can be relied on absolutely to distinguish identity.
I therefore follow Steve in thinking that in many cases there would 
be nothing that could be relied upon to be agreed on. Would it, in 
those circumstances, make sense to have a "bare" PSI?

Secondly, despite the related problems with information and knowledge 
systems, we all have a concept of existence (even if it is not always 
co-extensive), I would say as not just one property among others. 
Physical existence is just one property among others, to be sure, but 
existence of a concept - well, to me that is something different. And 
this will be reflected in any authority's set of PSIs: a PSI which 
identified something for which you didn't have any concept at all 
would be meaningless (to you), and couldn't be coherently attached 
(by you) to any structure in your knowledge base.

Thirdly, there is the question of how does one *in practice* 
distinguish between individuals. Of course we have to use properties 
related to the individual. But I'm happy to admit (though repeating 
myself) that no set of those properties is guaranteed to be effective 
for identification. Surely it's more fluid than that. If someone 
questions the validity of one set, we can move on to something else, 
until they are satisfied (or give up).

Thus, lastly, I agree that the separation may not be "clean", but I 
maintain the separability nevertheless. Indeed, how can we have a 
coherent discussion about which properties define identity *without* 
a notion of existence and identity separate from all those properties?

Simon

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