[topicmapmail] Are Facets Really Simple After All?

[Murray Altheim]

Kal Ahmed wrote:
 > On Mon, 2003-12-01 at 14:31, Murray Altheim wrote:
[...]
 >>No, not the first time. The first message of the thread I started
 >>on facets outlined two forms, Model A (the "RDF" model) and Model
 >>T (the "facet" model). Metadata about a topic is what I've been
 >>talking about all along. That's what RDF is: metadata about a
 >>single thing, a simple triple. The differentiation between "metadata
 >>about a Topic" and "metadata about a subject" I'm not making.
 >
 > I think you have to make that distinction. You talk about the colour or
 > time of creation of a topic, none of those things are properties of the
 > subject, they are properties of the topic that represents the subject.
 > You would not mean that "The time of creation of Paris is
 > 2003-11-23T11:34:55", regardless of how you expressed it you would mean
 > that "The time of creation of the topic who's subject is Paris is
 > 2003-11-23T11:34:55".

Okay, yes, I'm just getting lost in the thread here. Yes, there is
a distinction that must be made between subject and Topic. I'm just
not sure where to go from there.

 >>I'm
 >>going to have to answer Bernard, but in my first glance he mentioned
 >>that Topics are binding points. I agree with that. The triples in
 >>Model A are properties attached to the Topic. I consider those
 >>different than occurrences attached to the Topic. Occurrences are
 >>a specialized Association in the model that have their own special
 >>semantics and a special syntax in XTM, the <occurrence> element. We
 >>never created a <facet> element, nor did we a <property> element.
 >
 > I thought I had understood you to say that the values of these
 > properties apply to the topic, not the subject, but now I'm not at all
 > clear on that.

No, you're correct.

 > Is your <property> actually meta data about the topic (e.g. time of
 > creation of the topic, UI representation of the topic etc.)? If so, then
 > I agree with you that occurrences of the topic itself is not the way to
 > express this. If you're property is meta data regarding the subject
 > (i.e. meta data about Paris, not meta data about the topic representing
 > Paris), then I see no need for anything beyond occurrences and
 > associations to express this information. If you are saying that a
 > <property> is both of these things, then how do you propose to tell the
 > difference (how do I distinguish the creation date of the topic from the
 > creation date of the subject that the topic represents ?)

I think my hesitancy is about the middle area. I think that the
definition of "metadata" is really what's more in question. What is
meta at one level isn't at another, and perhaps I'm simply trying
to tackle more than is necessary. In my original note the idea of
"Model A":

   http://www.infoloom.com/pipermail/topicmapmail/2003q4/005406.html

there is an attempt to "do" RDF, i.e., create a way in XTM to express
the simple triples of RDF. What *is* metadata? I dunno. But the idea
of being able to express simple triples about a Topic without invoking
the whole Topic machinery is what I have heard people yearn for since
we did XTM (and during its development). It's what we dropped when we
decided not to implement facets in XTM. I think it might be dangerous
to attempt to distinguish between metadata about a Topic and metadata
about a subject for the same reasons that what is metadata at one level
isn't at another. All of this is likely very application-dependent, and
the approach taken in ISO 13250 (i.e., be very vague) could either be
considered a weakness or a strength.

I've been going back and forth on this partly because the discussion
warrants it, and partly because I am somewhat sitting on the fence,
trying to figure which side would hurt the least if I fell off.

Murray

......................................................................
Murray Altheim                    http://kmi.open.ac.uk/people/murray/
Knowledge Media Institute
The Open University, Milton Keynes, Bucks, MK7 6AA, UK               .

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