[sc34wg3] Individual contribution on the U.S. N.B. position o nthe progress ion of Topic Map standards

[Dmitry]

On Apr 1, 2004, at 1:38 PM, Mason, James David (MXM) wrote:

> I'm not a great theoretician, but my understanding of merging is that 
> it
> shoud be based somehow on subject identity. Now subject identity is a 
> sort
> of fuzzy thing in the current 13250 (I believe Patrick will soon have 
> more
> to say about this). We've had (controversial) approaches to merging 
> based on
> names. We've talked a lot about PSIs as a basis for identity. But the
> closest I've seen in something intended to become part of a standard 
> for
> defining how to establish identity is the discussion of  SIDPs in the 
> RM
> (that's a pretty bad sentence!). We've all fallen down on the job 
> here, from
> the original text of 13250 to the present because we've just assumed 
> we knew
> what identity was. If I remember my past life in algebras, 
> establishing (or
> postulating) a basis for identity is one of the first things that 
> needs to
> be done. I think that's one of the more valuable things the RM can
> accomplish, so we're not all depending on implicit assumptions.
>

I think that TMDM is now much closer to axiomatic definition of 
identity than RM.
TMDM has only one merging rule based on subject identifiers. Subject 
identifier in TMDM is an artificial construct created with only one 
goal - manage identity.

All other merging rules which people can imaging it is possible to 
express using this basic merging rule.

For example, let's say that we would like to introduce controversial 
base name  merging.

We can define following additional axiom in "extended" theory:

If X1 has BaseName Y1 in scope S
and  X2 has BaseName Y2 in scope S
Then X1 has the same subject identifier as X2

Now let's say that it is not enough. We can add new axiom:

If X1 has Internal occurrence O with  value  V in scope S
and X2 has internal occurrence O with value V in scope S
and  occurrence O is InverseFunctionalOccurrence
Then X1 has the same subject identifier as X2

As soon as data model is TMDM all possible merging rules are 
expressible as additional axioms which reduce identity management to 
only one basic  merging rule based on subject identifiers.

Situation is different if I decide to go outside of TMDM and move to 
the level of RM data model. In this case I cannot easily  construct 
rules described above. With TMDM I can use as much ontology commitments 
as I want to define new merging rules and TMDM has already rich 
semantics built-in.

With RM data model I am limited with syntactic low level constructs 
such as SIDPs and basic assertions. It is difficult
to express rich identity rules at this level (with almost zero 
semantics) because it requires to explain many other things first. What 
is a name in terms of RM DM?  What is an occurrence? What is scope? If 
I know answer for this questions I can easily define semantically 
meaningful identity rules even at RM DM level.


Dmitry