[topicmapmail] Are Facets Really Simple After All?

[Kal Ahmed]

On Mon, 2003-12-01 at 16:09, Murray Altheim wrote:
> Kal Ahmed wrote:
> > On Mon, 2003-12-01 at 15:31, Murray Altheim wrote:
> [...]
> >>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.
> > 
> > You are absolutely right, of course. What is meta data for some is
> > information for others, its a matter of perspective. To my mind we use
> > meta data to assist in searching, describing and classifying the
> > information that we really care about. Meta data is just information
> > that helps us work with the information that we want to work with.
> > Transferring that view to the topic map world. I would suggest that for
> > the most part, the information that we really care about (within the
> > domain of the topic map - I'm not discussing the resources that the
> > topic map links to as occurrences here) are topics, and has to be topics
> > because if we care about this information we are going to want to say
> > something about it. Then what ever we consider to be meta data can be
> > treated as either topics or occurrences - depending on whether or not we
> > believe this information to be something that someone else using the
> > same topic map will care about enough to want to say something about.
> 
> I think we are in complete agreement.
> 
> >> 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). 
> >
> > Thats true. But I think that the occurrences mechanism we have is much
> > more generally useful than simple triples.
> 
> Yes, but *perhaps* at the expense of what I've been calling semantic
> violence. With only a slight flourish of Johnny Deppish piratese.
> 

I think that if you mind the gap between the (pirate) map and the domain
being mapped, you should not be inflicting any violence on anything.

> >>It's what we dropped when we
> >>decided not to implement facets in XTM. 
> > 
> > Careful here. Facets in ISO 13250:2000 that did not make it into XTM 1.0
> > are not properties of topics, they are properties of resources. You
> > point to a resource and apply property value pairs to it. Sure, it could
> > be a mechanism for providing topic meta data (by pointing to the topic
> > element as the resource), but it was not principally created for that
> > purpose. The reason facets didn't make it into XTM was that it was felt
> > that if this resource is something you care about enough to want to
> > attribute  property/value pairs to it, then you should create a topic
> > that represents that resource and use occurrences. In other words, ISO
> > 13250:2000 facets are a short cut for reification and using occurrences.
> 
> Ah, yes, an important and correct distinction, and of course the "R" in
> RDF is for "resource".
> 
> I started to reply to your last sentence but then realized I was confused
> by it. Are you saying that ISO 13250:2000 facets are neither Topics nor
> occurrences? That they are something else, something not representable
> in XTM? I'm not quite following.

An ISO 13250 "facet" is a construct that allows you to tie a
property/value pair to a resource. Now, ISO 13250:2000 and ISO
13250:2002 are not clear on how this construct equates to
topics/occurrences. There may be a clear equivalence in some peoples
minds, but it is not documented in the standard.

To my mind, an if you use an ISO 13250 facet to apply the property/value
pair "Created=2003-12-01T16:29Z" to a resource
"http://www.techquila.com/resource.html", this is equivalent to creating
a topic whose subject address is http://www.techquila.com/resource.html
with an occurrene of type "Created" and a value that is the string
"2003-12-01T16:29Z". The only tricky part is that ISO 13250 allows you
to use menemonics for describing the property, rather than forcing you
to use a topic. But I see that more as an inconsistency in ISO 13250
that was corrected by the removal of mnemonics from XTM. (And I know
that there are those who do not see it this way).


>  I suppose I'm still curious to know how
> you'd "do" RDF in XTM, or if you'd not at all.
> 

What, you mean if I were forced to at sabre-point by a semantic pirate ?
;-)

Well, as you know there are different levels of modelling this stuff,
and as Lars Marius and others have shown in various papers over the last
couple of years, there is always more than one way to do this and it
ends  up being application specific.

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.

Cheers,

Kal
-- 
Kal Ahmed, Techquila
Standards-based Information Management
e: kal@techquila.com
w: www.techquila.com
p: +44 7968 529531