TM Stack: I Beg To Differ
Every now and then I see typical stack diagrams depicting the standards landscape in TM and in RDF land.
While the relationship between TMRM and TMDM is mostly represented correctly, that is, that TMDM constructs can be couched in terms provided by TMRM, the rest of the usual diagrams does not reflect my understanding.
TMQL, for instance, is not only building on TMDM constructs, its whole formal semantics is based on TMRM path expressions. That may not be visible to the TMQL user, but it is there.
And TMCL is purely defined in terms of TMQL expressions. That, in fact, is one of the significant differences relative to the RDF stack. There, OWL semantics is directly based on RDF model semantics. And SPARQL is defined on the RDF model as well.
I find the TM stack definitely leaner and more consistent, but there is this gaping hole I keep phantasizing about: TMOL.
At latest from Larsbot's TMCL tutorial it should have become clear that TMCL is a constraint language. That means that it has a destructive relationship with any topic map:
A TMCL schema defines conditions to be satisfied, only then the map is valid against that schema.
In other words, a TMCL constraint tastes like this:
If something is an instance of CAT, then that instance must also have an occurrence legs with the value 4 and another, utterance, with a value meow.
Otherwise this is bad for the relationship with the map.
OWL and other ontology languages work actually the other way round:
If something has an occurrence legs with the value 4 and another, utterance, with a value meow, then automatically it will be classified as instance of CAT.
It is derived and the author does not have to provide it manually.
OWL can only do the deriving part, TMCL only the constraining. (This is somewhat an oversimplification.) That is why there cannot be a straightforward transformation between them.
TMOL could cover the deriving part in the TM stack. If it existed ...