I'm trying to wrap my brains around the HQL and how it's implemented, under the covers. Any suggestions of where to look? I've poked at the javadocs, and tried to glean some information from the test tree, but am missing the big picture. Any leads on where to begin my quest for knowledge? I'm impressed with Hibernate's documentation for users, but I guess I'm looking for the playbook for folks who are interested in its development.

Have a look at source code n.s.h.hql package and the entry class QueryTranslator.java

More and more people have been asking for this, so it is certainly on my todo list to document internals. We had a session at JAOO going through this stuff (we should have videotaped it!)

Note: the current implementation of the HQL translator is NOT elegant. We will eventually re-write it to use a proper grammar + generated parser + AST. Currently it uses a pure-lookbehind, handwritten parser and no AST.