An introduction to program and thread algebra

We provide an introduction to Program Algebra (PGA, an algebraic approach to the modeling of sequential programming) and to Thread Algebra (TA). PGA is used as a basis for several low- and higher-level programming languages. As an example we consider a simple language with goto's. Threads in TA model the execution of programs. Threads may be composed with services which model (part of) the execution environment, such as a stack. Finally, we discuss briefly the expressiveness of PGA and allude to current work on multithreading and security hazard risk assessment.