This article is from the soc.history.medieval FAQ, by Stephan Schulz firstname.lastname@example.org with numerous contributions by others.
(That's me, Stephan Schulz answering. I have little knowledge
about genealogy, Schulz is about the third most frequent name in
Germany, and, due to the extensive resettlement of my ancestors
after WW2 I have lost nearly all contact to ancestors on the
Schulz side of the family. Someone else in the group probably
can help you, but please check the soc.genealogy.* groups first).