Let's evaluate performance algebraically

We discuss the benefits of using process algebras in the field of performance modeling and evaluation. We briefly present problems that have been tackled, theoretical results, and future developments. Many computing systems consist of a possibly huge number of components that not only work independently but also communicate with each other from time to time. Examples of such systems are communication protocols, operating systems, embedded control systems for automobiles, airplanes, and medical equipment, railway signaling systems, air traffic control systems, distributed systems and algorithms, computer architectures, and integrated circuits. The catastrophic consequences of failures, such as loss of human lives, environmental damages, and financial losses, in many of these critical systems compel computer scientists to develop formal description techniques for ensuring that these systems are implemented correctly despite of their complexity. Formal methods are conceived to allow the correctness of a system design to be formally verified because the design can be described in a mathematically precise fashion, correctness criteria can be specified in a similarly precise way, and the design can be rigorously proved to meet or not the stated criteria. Although a number of description techniques and related software tools have been developed to support the formal modeling and verification of functional properties of systems, only in recent years temporal characteristics have received attention. This has required extending formal description techniques by introducing the concept of time, represented either in a deterministic way or in a stochastic way. In the deterministic case the focus typically is on verifying the satisfaction of real time constraints, i.e. the fact that the execution of specific actions is guaranteed by a fixed deadline after some event has happened. As an example, if a train is approaching a railroad crossing, then bars must be guaranteed to be lowered on due time. In the stochastic case, instead, systems are considered whose behavior cannot be deterministically predicted as it fluctuates according to some probability distribution. Due to economic reasons, such stochastically behaving systems are referred to as shared resource systems because there is a varying number of demands competing for the same resources. The consequences are mutual interference, delays