If i'm not mistaken you'd want to select a person based on whether or not this person is enroled in a certain exam contest set.
This is a hibenate thingy, nothing to do with seam. Upon version 3.2.something you need to join everthing so it would be like this; which is the normal way you would do it in sql
SELECT person FROM Person as person INNER JOIN exam as person_exam INNER JOIN contestSet as person_exam_contestSet WHERE person_exam_contestSet.id = ..
should ofcourse be
INNER JOIN person.exam as person_exam etc