Element of Interaction :Touring Award Lecture.

The article presents information about semantic basis of concurrent computation delivered at Touring Award lecture by the author. Concurrency requires a fresh approach, not merely an extension of the repertoire of entities and constructions which explain sequential computing. It also describes efforts to find basic constructions for concurrency, guided by experience with sequential semantics. This works which led to a Calculus for Communicating Systems. It outlines a new basic calculus for concurrency. A theory of concurrency and interaction requires a new conceptual framework. Scott-Starchey approach to programming language semantics, a theory of domains, Shared Memory Model represents the active⁄passive distinction between components, by using differently shaped nodes. Static constructions and dynamic constructions are described. The meaning and values of sequential paradigm are described. Pi calculus and the naming or reference has been described. It was concluded that a basic model of concurrency is guided by a sequential paradigm. INSET: Sources and Related Work..