Handling RDF with a serach engine category structure

Dear Sir,

I'm a student in City University in Hong Kong and I'm dealing with a task 
which has to build an internal search engine to classify some inputted keywords into different category. I have download and study Jena, which from http://www.hpl.hp.com/semweb/download.htm, and I got some problem in handling RDF.

Knowing that the RDF used in Internet search engine is the most suitable tool for me to perform the task mentioned above, I've download the RDF ( 
structure.rdf.u8.gz) at the web http://dmoz.org/rdf.html and try to study it. 
However, it's structure is different greatly from the RDF structure introduced 
in Jena, so I have no idea on how to handle it. Would you kindly tell me how can I hanlde the structure like this? Looking forward to your reply, thx!

Best wishes,
Kevin Kwan from Hong Kong