Abstract:

The proposal presents extensions of specification language LOTOS in two directions: time consuming actions and performance evaluation constructions. Time consuming actions often seem to be more natural than instantaneous actions and they are well suited for real-time system specification and for its performance evaluation. The notions of beginning and termination of the time consuming action enable to impose time restrictions on beginning and termination times of activities. From performance evaluation point of view it is often important to know explicit how long a specific action has been executed (not when the action has been completed only). We have defined such a performance evaluation extension of LOTOS that can be used as a modelling language for performance evaluation of distributed systems. A semantics that expresses overlapping of time consuming actions in time is defined. A reduced transition system for the extension is defined. This reduction when comparing with original transition system has two advantages. First, the reduced transition system contains aggregated transitions that are a result of appearing many events in the same time instant. Second, this reduction eliminates some states. The reduction is essential for transition systems with actions of two scales of execution time: short and long actions. The greater the ratio of short actions to long actions is the greater the reduction of the number of states of the transition system is. By means of the reduced transition system we express the true concurrence semantics of our language. Our extension towards performance evaluation can be used as a basis for both simulation and analytic approaches.