OCL Specification v2.4.pdf

This clause introduces the Object Constraint Language (OCL), a formal language used to describe expressions on UML
models. These expressions typically specify invariant conditions that must hold for the system being modeled or queries
over objects described in a model. Note that when the OCL expressions are evaluated, they do not have side effects (i.e.,
their evaluation cannot alter the state of the corresponding executing system).
OCL expressions can be used to specify operations / actions that, when executed, do alter the state of the system. UML
modelers can use OCL to specify application-specific constraints in their models. UML modelers can also use OCL to
specify queries on the UML model, which are completely programming language independent.
Note - This clause is informative only and not normative.