Unified Modeling Language for Real-Time Systems Development

Specifying and designing real-time systems is a complex matter because real-time systems require logical correctness as well as timing correctness. Over the years several techniques for specifying and designing real-time systems have been developed, such as Finite State Machines, Petri Nets and Timed CSP. One of the latest notations for object-oriented specification and design is the Unified Modeling Language (UML). The question whether the UML is applicable for developing real-time systems is discussed in this paper. Three notions of time (ordered time, relative time and absolute time) are explained which can appear in real-time systems development. In a general applicable modeling language it must be possible to express timing requirements of all these three forms plus context timing requirements and general timing requirements. Furthermore the object model of the UML and the dynamic model of the UML in combination with an example of a watchdog timer are explained. The dynamic model of the UML can express ordered time, relative time, a form of absolute time and context timing requirements and not general timing requirements. Furthermore the separation of the specification phase and the design phase in the UML is discussed and some suggestions to improve the UML are given.