The Amsterdam Manifesto on OCL
  In November 1998 the authors participated in a two-day workshop on the Object Constraint Language (OCL) in Amsterdam. The focus was to clarify issues about the semantics and the use of OCL, and to discuss useful and necessary extensions of OCL. Various topics have been raised and clarified. This manifesto contains the results of that workshop and the following work on these topics. Overview of OCL. 
Steve Cook, Anneke Kleppe, Richard Mitchell, Bernhard Rumpe, Jos   Warmer, Alan Wills
cs.SE