The Object Constraint Language (OCL) is a declarative language for describing rules that apply to Unified Modeling Language (UML) models developed at IBM and is now a part of the UML standard.

• Initially, OCL was only a formal specification language extension to UML, but it may now be used with any Meta-Object Facility (MOF) and Object Management Group (OMG) meta-model, including UML.[2]
• OCL 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.