Tony Clark & Jos Warmer 
Object Modeling with the OCL [PDF ebook] 
The Rationale behind the Object Constraint Language

As part of the UML standard OCL has been adopted by both professionals in industry and by academic researchers and is one of the most widely used languages for expressing object-oriented system properties. This book contains key contributions to the development of OCL. Most papers are developments of work reported at different conferences and workshops. This unique compilation addresses many important issues faced by advanced professionals and researchers in object modeling like e.g. real-time constraints, type checking, and constraint modeling.