Control oriented specification languages

Specification is a formal description of what a system should do. Many techniques exist for specification. SDL language is a commonly used specification language developed by the communications industry. This language is best for specifying communication protocols and telephone systems. SDL specification includes states, actions and both conditional and unconditional transition between states. Since transition between various states is due to the internal and external events, SDL machine is known as event-oriented state machine. For state based specification, statechart technique is used. The statechart technique involves an event-driven model. Statecharts permits states to be grouped together to show common functionality. The two basic groupings used here are OR and AND. These languages are used in Traffic Alert and Collision Avoidance System (TCAS). TCAS is a collision avoidance system for aircraft. A TCAS unit fixed in an aircraft always keeps track of the position of other nearby aircraft. On a possible mid-air collision, TCAS unit use audio commands to suggest evasive action.