The Object Data Standard ODMG 3.0
R. Cattell, D. Barry, D. Jordan, C. Russell, et al. (Editors), The Object Data Standard ODMG 3.0, Morgan Kaufmann, 2000, ISBN 1-55860-647-5.
Two free sample chapters to download:
Chapter 1: Chapter 1: Overview
Chapter 2: Chapter 2: Object Model
(More about this book here)