The normal way to map a tree in a relational database is in one table.
Mapping the relationship in a separate table is more generic. You can add additional relationships (step-father, step-mother, godparents, etc.) without adding additional columns to the Person table. Some of the relationships could be one-to-many (marriages!) If you had to add a new column for every possible type of relationship it could get out of hand.
Also, you can add attributes to the relationship entity like relationship type, estranged=[true|false] or even effective/expiration dates (ouch! Somebody got disowned!).
Jason,
Hibernate In Action section 6.3 has a discussion on mapping associations with several examples. If you don't have a copy handy, you can try
chapter 8 of the Hibernate manual. If you have an existing database schema, you can use
Middlegen to reverse engineer the schema into a basic mapping file that you can tweak as necessary. This is most helpful when you have a complex, pre-existing schema.
Regards.