Question: Is it possible to only display particular category (e.g. 'homepage') posts on the Tumblr frontpage?

The other categories I want to be available using a 'redirect' page which.

Answer: 
I figured it out myself.
I still don't know the exact reason, but somehow the problem is caused by performing this code multithreaded and not by loading the ontology itself. When I run the code without multithreading, the loading only takes several seconds
I guess the slowness is inevitable if you are loading a huge ontology, but you can try and increase the memory allocated to Java as shown [here](http://www.wikihow.com/Increase-Java-Memory-in-Windows-7) so that at least you know the ontology will be loaded.