This document has quite a few diagrams and definitions which are very helpful.
Also in the same document the list of schemas for process communication documents is helpful:
ebXML Catalog of Common Business Processes
This is a little older from 2001, but still useful and includes a list of related processes in many different standard specs. This is a large document with a really long list of fairly granular processes.
Universal Business Language 1.0 ebBP 2.0 Business Process Definitions
This is more related to UBL 1.0, but is recent (from 2006) and useful. It is brief though.