The concept of interactive process is more general than the concept of interactive program. An interactive process is in essence a state transition system, and is specified in exactly the same way as interactive programs earlier. Interactive programs consist of an arbitrary number of interactive processes. O. It is shown that interactive processes can be evaluated purely sequentially, in an interleaved fassion, but also in parallel. Both forms of communication integrate smoothly in the system.
Data sharing is a form of communication by a common piece of global data.
Access to this data is restricted to one process at a time. Provided that interactive processes have the identification of a given interactive process they can send messages to that interactive process. State transition systems prove to be a useful and generally applicable concept. We have applied them as a basis for interactive processes and data sharing. Taking a slightly different point of view one can regard state transition systems also as objects of the object-oriented paradigm.