Boning up on Hibernate and JPA, makes me think about the history of relational databases.

Facts like these can be gleaned from sources such as Wikipedia:

Ingres begat Postgres.

Sybase was originally a clone of Ingres.

MS-SQL server came from Sybase.

Oracle may have initially been a clone of IBM System R.

Informix came out of nowhere.

What I'd like to find is a nice genealogical chart of all this stuff, like the unix timeline, or the computer languages history.