What is Object Constraint Language

The Object Constraint Language (OCL) is a declarative language for describing rules that apply to Unified Modeling Language (UML) models developed at IBM and now part of the UML standard. Initially, OCL was only a formal specification language extension to UML. OCL may now be used with any Meta-Object Facility (MOF) Object Management Group (OMG) meta-model, including UML. The Object Constraint Language is a precise text language that provides constraint and object query expressions on any MOF model or meta-model that cannot otherwise be expressed by diagrammatic notation. OCL is a key component of the new OMG standard recommendation for transforming models, the Queries/Views/Transformations (QVT) specification.

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Different ways MDriven relies on OCL

• As constraint definition on a class
• As description of derivation rule on derived attributes
• As description of derivation of derived associations
• As ViewModel columns and Nesting definitions
• As definitions for Visible and Enable state for ViewModel columns
• As expression of style information on ViewModel columns
• As expression for object presentation on classes
• Action Enable expression
• State machine Guards

MDriven relies heavily on OCL and it is a very powerful tool to describe constraints, actions and transformations in your model.

OCL expression must be without side effects. It is a query language and as such it is not expected to change data as the language is applied. In MDriven we do however want to change data when appropriate – so we use the exact same syntax as OCL in something we call EAL – ExtendedActionLanguage.

Methods

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