RE: [Tm4j-developers] Association.ofType()

[Kal A. <ka...@te...>]

> > C is only an association of type B. B is an instance of the
> class A, but A
> > is not a superclass of C. Sounds confusing ? :)
> >
> > The <instanceOf> element (which translates to the type or types
> attribute)
> > specifies a class-instance relationship. Topic maps are a powerful
> > information modelling tool because they allow a topic to be
> both a class and
> > an instance of a class.
> >
> > You can model the subclass-superclass relationship by using an
> association
> > with the XTM-defined PSIs which you will find declared as constants in
> > com.techquila.topicmap.PSI. To get the supertypes of a topic,
> you need to
> > first go to its type(s) and then for each of them, traverse the
> > subclass-superclass association to find superclasses.
>
> Okay, sound reasonable. Interesting point: What happens with
> cyclic dependencies ? E.g. A instanceof B, B instanceof C,
> C instanceof A. Nobody bars you to model this, but it could cause
> problems while processing.
>

It is true that you could get problems from this kind of dependancy loop -
though I think that different applications would have different ways of
wanting to handle it. I don't think that TM4J would have a problem - there
are relatively few functions which perform any kind of traversal, but an
editing application or a display application would need to be able to handle
cycles in the topic map model.

One thing that would be useful in a suite of topic map tools would be
utilities to discover these kinds of problems and report on them - perhaps
something like that should go into the command-line utilities package. This
raises another question: What other kinds of problems should a "topicmap
lint" application report on ? I would be interested in peoples' thoughts on
this...

Cheers,

Kal