As far as I understand, this package 'only' handles an ontology ( a graph of classes) but it is not designed to create some instances (e.g: http://en.wikipedia.org/wiki/Charles_Darwin is an instanceOf the class 'MY_ONTOLOGY:Human' )
If you only want to find all the terms in the ontology, the documentation says:
To find all ontology terms two
functions can be used: getAllTerms
Yes, this is what I have come to realize. Just surprised that there isn't a function for handling instances...
So far there hasn't been much demand for this functionality, please feel free to request it via https://lists.sourceforge.net/lists/listinfo/ontocat-users if still interested.