In addition, constraints should be expressed in natural language in the accompanying documentation of the model".
The OCL expression is important for implementation (but not mandatory), while the natural language expresion is important for human understanding of the model.
NOTE: The Schematron language may be used to express OCL constraints as part of the XML Schema representing the GML application schema.".
The use of OCL in the context of UML and in the field of Model-Driven Engineering (MDE ) has originated an increasing interest in tools supporting OCL from several scopes.
Maude is a formal language with a wide number of tools to analyze specifications and there are a number of tools and papers proposing the use of Maude as a candidate to deal with UML specifications.
This can be done by adding a note to the diagram and linking it to the element.
The Object Constraint Language (OCL) is a declarative language describing rules applying to Unified Modeling Language (UML) models developed at IBM and is now part of the UML standard.