[topicmapmail] Fragmented XTM for web metadata, and some ontology?

[Thomas B. Passin]

[Murray Altheim]

> I don't think it's appropriate semantically to include properties
> of a given topic as occurrences of that topic -- it's just not
> sensible, doesn't "read" right to me. You yourself stated the sentence:
>
>      "here is the resources"
>
> which is essentially saying "here are the untyped values". Since we
> want to both name and type our values, and because occurrences don't
> have names, each facet is a topic.
>

I really do not agree with Murray here at all.  First of all, occurrences
__can__  have types - they have their instanceOf topics.  If you argue that
we have no standard way to assign a datatype to any topic except in prose, I
agree, but I think we should be able to state the datatype of an occurrence
value.  I have posted on this before.  Two ways to do so are to specify its
MIME type or to us an XML Schema data type, as you can now do in the latest
drafts of RDF.

Anyway, using a topic instead of an occurrence does not solve the problem of
data type, because we cannot say that a particular topic is of some data
type either - at least, we can only do it in prose.

So we can have named and typed occurrences (modulo the data type issue), and
so an occurrence can perfectly well represent a property name/value pair.  I
use them like that all the time.

If you are a purist, you probably think that an occurrence should be
considered a syntactic shorthand for a particular style of association.  If
you think that way, go ahead and make up topics and associations.

Not only that, for most people, there is a real distinction between
properties and associations.  Properties have Pierce's "firstness", while
relationships have "secondness" (if I understand that right - feel free to
reread Sowa about this).  Therefore they should be modeled differently.  The
only other modeling construct we have besides the association is the
occurrence.

Finally, as a practical matter, if I model my properties as associations, it
is much harder for me to know which topics are supposed to be properties and
which ones are not.  It would be really hard to make a list of the
properties of some topic but not bring in other associated topics.  On what
basis would you be able to distinguish the two?  You do not want to have to
know beforehand which topic types are supposed to be properties.  Well, you
could give them (their names) a "properties" scope, that would work, I
suppose.  Sounds like a hack, though.

So I plump for using occurrences for properties.  Maybe there are some
exceptions, and if you want to be able to say anything else about those
property instances, obviously you have to make topics for them.

Cheers,

Tom P