[topicmapmail] Are Facets Really Simple After All?

[Murray Altheim]

Thomas B. Passin wrote:
> Kal Ahmed wrote:
> 
>>However if I were to transcode property/value pairs which are clearly
>>properties of subjects described by a topic in my topic map, I would use
>>associations for those property/value pairs where the value is a
>>resource which is the subject or object of other statements, and
>>occurrences for those property/value pairs where the value is a resource
>>that does not appear in any other statement or where the value is a
>>literal string. But thats just a rule of thumb.
>
> In one way of looking at things, properties are named values that relate 
> to a single subject, whereas associations relate two (or more) subjects. 
>    With this view, you would be very interested in using a different 
> mechanism for properties and associations, because you see them as 
> fundamentally different kinds of things.
> 
>  From another point of view, properties and associations are both 
> predicates.  The first kind has one argument (besides the subject), the 
> second has two or more.  In this view, there is no essential difference 
> between properties and associations.
> 
> I usually prefer the first way, but it depends on what you want to to. 
> Here are three conceptual graphs from p. 31 of John Sowa's book 
> Knowledge Representation (relations are in parens, concepts are in 
> square brackets) -
> 
> 1) (Red) -> [Ball]
> 2) [Ball] -> (Attr) -> [Red]
> 3) [Ball] -> (Chrc) -> [color:Red]
> 
> Here, "Chrc" is short for "characteristic". and "Attr" is short for 
> "Attribute".
> 
> It seems to me that we cannot quite do either 2)  with topic maps, 
> because we cannot use a topic as the value of an occurrence.
> 
> We could do 3) as an occurrence, I think, by creating a topic "color" 
> and giving an instance of it an occurrence whose type would be "value" 
> and whose value would be "Red".  The "Chrc" relation would be implied by 
> the use of the occurrence.
> 
> We can do 2) if we create a topic for "Red".
> 
> Hmm... anybody want to comment?

Well, you've hit upon the definition of "property" used in a lot
of KR literature: monadic predicates, right out of predicate calculus.
Two or more arguments changes the word from "property" to "relation";
the latter being the Topic Map synonym for "association". [Since you're
quoting from Sowa, this is on page 469.]

So, properties in Topic Maps wouldn't involve more than one Topic.
This seems to agree with the idea of facets (properties) in ISO 13250.
At least that's the way I usually have seen this too.

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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