Four-Valued Logic in UML/OCL Models: A “Playground” for the MVL Community

The Unified Modeling Language (UML) together with the Object Constraint Language (OCL) are the description means for modeling and specifying, e. g., software systems in early stages of the design. They allow to define components, their relations, and constraints of a system while, at the same time, hide precise implementation details. Despite providing a “blueprint” for the desired systems, UML/OCL descriptions also allow for an early validation and verification of the design. However, an often overseen feature of UML/OCL is that it explicitly allows for the consideration of irregular variables assignments such as null and invalid-yielding a four-valued logic in the current UML/OCL version. In this tutorial, we provide an overview on this feature and the resulting four-valued UML/OCL logic. More precisely, we are providing a review of the corresponding description means as well as existing methods that allow for a validation and verification of the corresponding models. By this, we are aiming to introduce those UML/OCL descriptions and methods to the MVL community in order to trigger new directions for research and application.