A reactive system is one that is in continual interaction with its
environment and executes at a pace determined by that environment.
Examples of reactive systems are network protocols, air-traffic control
systems, industrial-process control systems etc. Reactive systems are
ubiquitous and represent an important class of systems. Due to their
complex nature, such systems are extremely difficult to specify and
implement. Many reactive systems are employed in highly-critical
applications, making it crucial that one considers issues such as
reliability and safety while designing such systems. The design of
reactive systems is considered to be problematic, and p.oses one of the
greatest challenges in the field of system design and development. In
this paper, we discuss specification-modeling methodologies for reactive
systems. Specification modeling is an important stage in reactive system
design where the designer specifies the desired properties of the
reactive system in the form of a specification model. This specification
model acts as the guidance and source for the implementation. To develop
the specification model of complex systems in an organized manner,
designers resort to specification modeling methodologies. In the context
of reactive systems, we can call such methodologies reactive-system
specification modeling methodologies.