Basic resources

Official OCL language specification

OCL Book
The book 'The Object Constraint Language: Getting Your Models Ready for MDA, Second Edition' provides a thorough and up to date introduction to the topic

Definition of OCL in Wikipedia

Software

Octopus
Octopus is a plugin for the Eclipse IDE and offers the capability to edit and verify OCL-expressions in the context of a given UML-model. Models are specified in a tool-specific language but export-scripts are available for Rational Rose and MagicDraw.

OCLE - Object Constraint Language Environment
This is a comprehensive OCL evaluation and model checking tool that works on top of an XMI-exported model. It was created and is supported at the Babes-Bolyai University, Romania.

Dresden OCL-Toolkit
The 'Dresden OCL Toolkit' is a suite of Java programs and libraries to validate OCL code and to generate Java source code.

Miscellaneous

Precise UML (puml) mailing list
The puml mailing list is a great place to discuss OCL issues online.

OCL tutorial on parlezuml.com
This is a very good introduction to OCL (pdf) written by Jason Gorman.

A Rational Rose model with the UML 1.5 and OCL 2.0 metamodel
If your are interested in exploring these metamodels, this is a nice supplement to the official specifications.

OCL Wiki
A Wiki about OCL.

Article by Gary Pollice on OCL
This article demonstrates the added value of using OCL to enrich UML models and also makes a suggestion how to use OCL to specify testcases.

Website of Klasse Objecten
This site is maintained by the original inventor of OCL, Jos Warmer. It offers some general information about OCL.