Date:   Thurs., 11 Mar. 1999
Time:   1 p.m.
Place:  CS seminar room

                       STATECHARTS VIA PROCESS ALGEBRA


                               Gerald Luettgen
                                    ICASE
                                 NASA Langley


Abstract: Statecharts is a visual language for specifying the behavior of
reactive system.  The language extends the traditional notation of
finite-state machines with concepts of hierarchy, so that one may speak of a
state as having substates; concurrency, thereby allowing the definition of
systems having simultaneously active subsystems; and priority, so that one may 
express that certain system activities have precedence over others.
Statecharts has beeome popular among engineers as a design notation for
embedded systems, and commercially available tools provide support for it.
Nevertheless, precisely defining the semantics of the language has proved
extremely challenging.

In this talk I present a new, process-algebraic semantics of Statecharts.  Our
approach invovles a new process algebra, called Statecharts Process Language
(SPL), which is inspired by timed process algebras.  Like other process
algebras, SPL possesses a simple, inductively defined semantics; we
nevertheless show that it is expressive enough for encoding Statecharts in a
structure-preserving and semantics-preserving manner.  We also establish that
an existing equivalence, bisimulation, when applied to SPL, preserves
Statecharts semantics.  This work may therefore be seen as anchoring
Statecharts withing the process algebra field, thereby allowing techniques and
tools developed in this community to be applied to it.

-- 
Rance Cleaveland (rance@cs.sunysb.edu)
Tel:   (516) 632-8448 (voice), (516) 632-8334 (fax)
WWW:   http://www.cs.sunysb.edu/~rance
Post:  Dept. of Comp. Sci., SUNY at Stony Brook, Stony Brook, NY 11794-4400