Academy of Sciences. Updated 2013.10.13.

Abstract: The paper contributes with a concept of process viewed as a model of a run of a system (discrete, continuous, or of a mixed type), with operations allowing to define complex processes in terms of their compo-nents, and with the idea of using the formal tools thus obtained to define the behaviours of concurrent systems. A process may have an initial state (a source), a final state (a target), or both. Processes of which one is a continuation of the other can be composed sequentially. Independent processes, i.e. processes which do not disturb each other, can be composed in parallel. Processes may be prefixes, i.e. independent components of initial segments of other processes. Processes and operations on processes are represented by partially ordered multisets of a certain type and operations on such multisets. Processes in a universe of objects and the sequential composition o