[topicmapmail] RE: back to the lists

[Murray Altheim]

Bernard Vatant wrote:
> Martin  Bryan wrote:
> 
> Note that I wrote :
> 
> " Expressivity of OWL is flexible enough to express a *wide variety* of
> TM constraints."
> 
> And you answer :
> 
> " I don't see this as being helpful in describing *all of the
> constraints* TMCL is supposed to provide."
> 
> I don't know what "all of the constrains" means, and a big issue indeed
> is to define the limits of TMCL. That's why I said *a wide variety*.
> 
> The example you give is maybe borderline one ...
> 
> "Relationship A must have an X in role R and a Y in role Q and that no
> two A relationships with X can have the same Y."
> 
> I would gladly take the challenge to try and express it in OWL (I don't
> see why it could not) but please make it more accurate in its
> expression: Does A represent an individual association? Or an
> association type? Do X and Y represent an individual topic? Or a class?
> Does "an X" means "exactly 1 X"? Or "at least 1 X"? etc ...
> 
> In any case, and even supposing effectively that OWL cannot express that
> kind of specific constraint, I think dismissing a language simply
> because it cannot handle such and such "ad hoc" tricky situation is not
> a correct approach. I would prefer to explore what OWL *can* express,
> starting from basic needs that are now expressed in real use cases by
> implementers an their customers, and see if more is needed that can't be
> expressed.
[...]

Bernard,

Unless I'm mistaken (and I'm happy to hear arguments as to why I
might be), the whole discussion about OWL being used to constrain
topic maps ignores the difference between typical XML and RDF
processing and topic map processing.

If one converted an XTM document into RDF (demonstrably possible)
it would still need conformant topic map processing, which is
different than validation or markup constraint checking. Moving
up the lexical/syntactic level of processing, can you base a topic
map constraint language on something that can't support topic map
merging? At what level does OWL function?

And as Martin added in "Corollary A"

    A. You don't gain anything by showing that you can do what
       can be done as easily some other way

[Martin, if you were a priest, I'd be in your church!]

What does one gain by using OWL if TMCL (which doesn't complicate
things by introducing RDF, RDF Schema, XML Schema, XML Namespaces,
etc.) do the trick? Using OWL may be a politically smooth move,
and make management feel warm and cuddly, but it doesn't translate
technically as a good solution to the problem, IMO. I've been
thinking about ontologies-in-topic maps for about two years, and
there's a lot of other options than the description logics of OWL.
A one-size-fits-all approach to computer-based ontologies is a
compromise at best.

I'd prefer to concentrate on a constraint language designed for
topic maps, expressed in a suitable syntax for topic maps. Then
again, I've never been one to jump on a bandwagon simply because
it's moving. It may be going over a cliff, and you can't tell
unless you're either driving or up with the driver. OWL-for-OWL'
sake is not a compelling argument.

I just keep hearing the boundaries between lexical, syntactic,
semantic, between XML parsing and topic map processing, all being
blurred within this discussion, and the product is a lot of
confusion (at least to me).

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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