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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.

Learn more with ☛ OCL Video Tutorials

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.


Seeking the database with OCLps


Certain important constructs


More articles:

Unique constraints on 1 to 1 links



Understanding OCL with reference to SQL

Custom types and custom operations in OCL

A few words on linq

OCL by example