Executing query on sub node?

Hi,

I was just wondering if it was possible to execute a query on a paricular subnode?

For example my structure is JCR_Root/categoryX/languageX/data1/..

I know the category and language nodes, so I want to execute the query on the set of data child nodes, but in my code it seems I can only execute the query on the whole JCR_root e.g.

QueryManager qMgr = session.getWorkspace().getQueryManager();
QueryResult result = qMgr.createQuery(xpathQuery, Query.XPATH ).execute();

then I need to iterate through the results to find the relevant data nodes.

Is there a better way to implement a more fine tuned search? And if so would this be more efficient?

Thanks,
David.