UML and the formal development of safety-critical real-time systems

The Unified Modeling Language (UML) is fast emerging as a de-facto standard for modelling object oriented systems. Like other software engineering methods, UML provides a set of graphical and textual modelling tools that aim to provide a common understandable language for developers and customers. However, UML has gone much further than previous methods in encouraging conformance of use. In particular, it provides a semantics document which aims to precisely describe the structure and meaning of the language. Recently, UML version 1.1 was accepted by the Object Management Group as a standard notation for object oriented analysis and design. Because of its growing popularity and the fact that it supports a number of real time facilities, there is a growing interest in applying UML to real time systems. Developers of safety-critical systems are also interested in UML because it claims to offer greater formality than other OO methods. There is hope that UML can provide a user friendly replacement for traditional formal notations. The article examines some of the issues associated with adopting UML for the development of safety-critical, real time systems. In particular we describe the current version of the language and its semantics (version 1.1) and explore its suitability as a basis for the formal specification of such systems. We then discuss some of the issues regarding formal refinement and deduction of UML models.