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: 
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.
If you are seeing the problem only when running the code in a multithreaded environment, there is a chance you stumbled upon some OWL API bugs in that respect, in the past this has been caused by HashMaps used as caches in various places and causing threads to get stuck if a change to the map happens at the same time as a read access.

200 classes is a fairly small ontology, so it should take seconds. If you can reproduce this situation consistently, please report it as a bug on github or on the OWLAPI mailing list.