1.6 Summary

OCL is a language that can express additional and neccesary information about the models and other artifacts used in object-oriented modeling, and should be used in conjunction with UML diagrammatic models.

Much more information can be included in the specification (the model) using the combination of OCL and UML than through the use of UML alone. As you have seen, even in very simple examples, many essential aspects of the system cannot be expressed in a UML diagram. This information can only be expressed in the form of OCL expressions.

The level of maturity of the software process is raised by building a UML/OCL combined model. Tools that simulate a system, generate tests or source code from a model, and tools that support MDA need more detailed and more precise models as input. The quality of the output of these tools depends largely on the quality of the model used as input.

Tools that generate tests and source code from UML/OCL make the development process more efficient. The time invested in developing the UML/OCL models is regained during the subsequent stages of development.

OCL is a precise, unambiguous language that is easy for people who are not mathematicians or computer scientists to understand. It doesn't use any mathematical symbols, while maintaining mathematical rigor in its definition. OCL is a typed language, because it must be possible to check an OCL expression included in a specification without having to produce an executable version of the model.

OCL is a declarative, side-effects-free language; that is, the state of a system does not change because of an OCL expression. More importantly, a modeler can specify in OCL exactly what is meant , without restricting the implementation of the system that is being modeled . This enables a UML/OCL model to be completely platform-independent.