The Free On-line Dictionary of Computing (30 December 2018):

Object Constraint Language

    (OCL) A formal specification language extension to
   UML.  The Object Constraint Language is a precise text
   language that provides constraint and object query
   expressions on an object-oriented model that cannot
   otherwise be expressed by diagrammatic notation.

   OCL supplements UML by providing expressions that have neither
   the ambiguities of natural language nor the inherent
   difficulty of using complex mathematics.

   OCL is a descendent of Syntropy, a second-generation
   object-oriented analysis and design method.  The OCL 1.4
   definition specified a constraint language.  In OCL 2.0, the
   definition has been extended to include general object query
   language definitions.

   OMG UML Home (http://uml.org/).

   Rational UML Resource Center
   (http://rational.com/uml/index.jsp).

   OCL 2.0 Submission to UML
   (http://omg.org/docs/ad/03-01-07.pdf).

   (2003-11-15)