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What is Object Constraint Language?

The Object Constraint Language (OCL) is a declarative language used 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, but now it may now be used with any Meta-Object Facility (MOF) Object Management Group (OMG) meta-model, including UML. It 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 a constraint definition of a class
  • As a description of the derivation rule on derived attributes
  • As a description of the derivation of derived associations
  • As ViewModel columns and Nesting definitions
  • As definitions for Visible and Enable state for ViewModel columns
  • As an expression of style information on ViewModel columns
  • As an expression for object presentation of classes
  • As Action Enable expression
  • As State machine Guards

MDriven relies heavily on OCL which is a very powerful tool for describing constraints, actions, and transformations in your model.

OCL expressions 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. We use the same syntax as OCL in something we call EAL – Extended Action Language.

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