**Part 2**

**Specification and Verification** 

28 Will-be-set-by-IN-TECH

94 Real-Time Systems, Architecture, Scheduling, and Application

van den Heuvel, M. M. H. P., Holenderski, M., Cools, W., Bril, R. J. & Lukkien, J. J. (2009).

*Systems Symposium (RTSS)*.

Virtual timers in hierarchical real-time systems, *Work in Progress session of the Real-time*

**5** 

*Poland* 

**Specification and Validation of Real-Time** 

**Systems Using UML Sequence Diagrams** 

UML (OMG, 2011) is considered as a contemporary standard in information systems development. Being a graphical modeling language it offers a family of diagrams that may be used for specification and designing of information systems. Sequence diagrams, being a part of the family, are very often used to specify functional requirements of the developed systems and are typically associated with the use case realizations in the logical view of the system under development. They show how actors involved in the scenario representing a use case realization cooperate with system's objects. Therefore, the meaning of a sequence diagram is a set of scenarios, each describing interaction between objects of the designed system and its environment. Semantics of sequence diagrams is defined informally in plain language, and, additionally, the definition is limited to the interpretation of single diagrams. But in nontrivial cases a set of sequence diagrams is necessary to give a complete specification of the system's behavior, and therefore the interpretation of the set of such diagrams is needed. Since UML has informal semantics, a set of sequence diagrams brings some interpretation problems. The problem becomes even more difficult when the real-time systems

are designed when numerous time constraints are associated with the diagrams.

be analyzed against its consistency and completeness.

stereotyped combined fragments.

Hence, the primary aim of the chapter is to give a precise interpretation of a set of sequence diagrams with time constraints. The formal interpretation is necessary to construct programming tools supporting validation of the systems' behavior specification, and possibly prototyping of the systems. The chapter demonstrates how the set of scenarios specifying system's behavior may be derived from the set of sequence diagrams, and how this set may

Another aim of the chapter is to propose an approach to real-time systems specification. Real-time systems have some peculiarities. For example, a typical task for a real-time system is to track the events from its environment and then responding to them, within imposed time constraints, through the generation of new events targeted to the environment. To follow such schemata, we propose to extend the UML sequence diagrams with new kinds of

A specific methodological aspect of real-time system specification is also considered. Namely, very often, in addition to an explicit description of the behavior of the system, additional properties such as safety and liveness, are taken into account. Usually, the

**1. Introduction**

Zbigniew Huzar and Anita Walkowiak

*Wrocław University of Technology, Institute of Informatics* 
