[sc34wg3] Topic names and occurrences in the TMDM

Murray Altheim sc34wg3@isotopicmaps.org
Thu, 29 Sep 2005 21:00:54 +0100

Jan Algermissen wrote:
> Murray,
> On Sep 29, 2005, at 6:56 PM, M.Altheim wrote:
>>Just a question that came to mind whilst reading the section
>>on Topic names in section 5.4 "Topic name items" of the TMDM:
>>   [...]
>>   Essentially, a base name is a specialized kind of occurrence.
>>To my mind, names are not a specialized kind of occurrence at
>>all -- names, occurrences and roles played in associations are
>>the three kinds of topic characteristics. Topic names and
>>occurrences are peers in that taxonomy; names are not a subclass
>>of occurrence, which would imply that a name is an occurrence of
>>the Topic, not a characteristic of it. That doesn't make sense
>>to me.
>>Clarification, please...
> Since TMDM suggested practice seems to be to express attributes of  
> subjects (age, height, eye-color, department number etc.) as  
> occurrences and since a name is just a special kind of attribute it  
> seemms logical to say that a name is a special kind of occurrence.

No, it doesn't seem logical at all. Please don't include yet another
term with "attribute". Let's simply call it what it's been called all
along in Topic Maps: a Topic characteristic. We could step out to a
more general knowledge representation language and use property, but
since we're talking about the Topic Map model, we might stick with
the language already extant.

Now, if we have a Topic called "Person", then a Person's age, height,
eye colour, etc. are just [typed] characteristics of Person, not
occurrences of "Person". You and I are occurrences of Person, our
names and eye colour are not. They are our characteristics.

I literally today answered this same question regarding names in the
Common Logic list. Names are characteristics (aka typed properties)
of an entity. A property relation is a unary predicate (a 1-ary
relation with the entity, i.e., in Topic Maps, a typed Association
between a Topic and its characteristic).

Unless the fundamental model of Topic Maps has changed since 2000 I
don't follow the logic of this at all. The language is screwy.

> Subject Indicators and Subject Address are then, BTW, also just  
> occurrences.

Sorry, but that's also screwy. Anything to do with "subject" is
a part of a Topic's identity-forming characteristics. Occurrences
do not form identity except in the most remote sense of the class
created extensionally by the members of its class, but I seriously
doubt too many people would ever do that using Topic Occurrences,
nor do I sense that this was the intent here.

There was a time when everything was a Topic, and now we've reached
a time when everything is a Topic Occurrence. *sigh*

> I have allways wondered what the benefit of four constructs for  
> things that are just semantic variations of a basic functinality  
> could be....seems awkward to have to implement basically the same  
> thing four times....

If you've read the graph theory description of Topic Maps you'd
see that the simplifications we used were to make the model
usable by humans. We could have decided not to have a Topic's
characteristics be anything special, forcing them to be explicitly
created via typed associations, but it's really a hell of a lot
easier to use that tiny bit of syntactic sugar. I would on the
contrary think it would have been *incredibly* awkward to have
devolved the current model into a more basic graph structure --
nobody would ever want to look at a Topic Map. This reminds me
of the RDF renditions of XTM documents. Yes, it can be done, but
no, it's not very useful.

There are humans involved in this stuff. These shorthands are

> Oh well...does anybody care?

I suppose one can take a nihilistic approach to ontology definition,
but I don't. It really bugs me when language is turned upside down
or distorted. Some of the knowing corruptions of legacy terminology
in RDF are terrible, as if somebody didn't do any homework. We don't
need to do the same in Topic Maps.


Murray Altheim                          http://www.altheim.com/murray/
Strategic Services Development Manager
The Open University Library and Learning Resources Centre
The Open University, Milton Keynes, Bucks, MK7 6AA, UK               .

        believe that everything is for
        you until you discover
        that you are for it
                               "The Robin and the Worm" by Don Marquis.