An Introduction to the Object Constraint Language (OCL)
Anneke Kleppe, Jos Warmer · Technology of Object-Oriented Languages and Systems · 2000
Visual modeling languages are appealing because picture tells more than a thousand words. The UML is such a visual language and is well known for its graphical notation and diagramming techniques. However, pictures often only tell half of the story and additional information needs to be captured in a different way. For this reason the UML includes the Object Constraint Language (OCL), a textual language, which allows a UML modeler to specify these additional constraints.