[sc34wg3] SAM-issue term-subject-identity

[Marc de Graauw]

* Ann M Wrightson

| 1. Yes, the term is needed, since it is a "co-ordination point" for the
| various arguments about when topics should be merged - including TNC, since
| the argument there is:
| two topics having the same name in the same scope, is sufficient evidence to
| consider their subjects to be identical.
|

I think you do not see my point.

I would say in the case you describe in your last sentence, we have sufficient
evidence to believe those two topics have one and the same subject. We do not
believe: the two topics have two subjects which are identical.
So my point is: either two topics have the same (one) subject, or the two topics
have two non-identical subjects. I have absolutely no problem with defining when
two topics represent the same subject, on the contrary, I agree this is
essential.

My belief that saying 'two subjects are identical' is wrong is inspired by
Freges conception of identity statements. He says, quite rightly I believe,
identity statements are made between names (or definite descriptions, which
uniquely identify an individual) i.e.:
'The morning star = the evening star'
'George W. Bush = the president of the USA'

What such an identity statement means is: the two names refer to the same thing
(have the same extension).[1]

Now the case in topic maps is fairly similar. We have subjects and subject
identities. Subject identities are like names: they are (in XTM)
<subjectIdentity> elements with content. Subjects are not like names. They do
not occur anywhere in a Topic Map, they are what is referred to by the
<subjectIdentity> element. <subjectIdentity> is in a sense a name of a subject.
If we follow this train of thought, it makes sense to say of two
<subjectIdentity> elements S1 and S2: S1 is identical to S2 (S1 = S2). In this
case, the represent the same subject. It also makes sense to say: NOT( S1 = S2),
in which case they represent two different subjects.

| 2. The notion of subject identity should be carefully and explicitly
| defined, since this definition determines a v. important aspect of topic map
| behaviour - including  the vulnerability of a topic map to rogue added
| information.
|

On further reflection I agree my suggestion to drop the term 'subject identity'
was a bit silly.

<skipped & agreed>

| 5. Here's my candidate for a sufficient case for considering two subjects to
| be identical:
|
| Two subjects A & B are identical if (and only if): considering all

I would say: "Two subject identities A and B are identical iff ...",
or: "Two subject identities A and B refer to the same subject iff ...".

Marc

[1] Those who find this interesting and are unfamiliar with it can read
paragraph 1 of my XML2001 paper:  http://www.marcdegraauw.com/whatisis.pdf