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
Your ontology is not that big (if 200 classes - big ones according to literature have over 300'000 classes) and you shouldn't encounter any memory problem using the OWL-API on modern machine (at least 2 Go of memory).

How to solve the issue:

* Make sure the JVM has enough memory allocated to it: Use the `-Xmx` and `-Xms` flags.
* Load the file from the system (example `/home/foo/bar.owl`) rather than from `localhost` proxy.
* You mentioned thread problems: Make sure only one thread reads the file at a time. The API takes care of threading the reading for you.