Interactive computation

de Scott A. Smolka, Peter Wegner

Interaction is an emerging paradigm of models of computation that re?ects the shift in technology from mainframes to networks of intelligent agents, from number-crunching to embedded systems to graphical user interfaces, andfromprocedure-orientedto object-baseddistributedsystems.Interacti- based models di?er from the Turing-machine-basedalgorithmic models of the 1960s in interesting and useful ways: ProblemSolving:Models ofinteractioncapturethenotionofperforminga task or providing a service,ratherthan algorithmicallyproducing outputs from inputs. Observable Behavior: In models of interaction, a computing component is modeled not as a functional transformation from input to output, but rather in terms of observable behavior consisting of interaction steps. For example, interactions may consist of interleaved inputs and outputs m- eled by dynamic streams; future input values can depend on past output values. Environments: In models of interaction, the world or environment of the computationis partofthemodelandplaysanactivepartinthecompu- tion by dynamically supplying the computational system, or agent, with inputs, and consuming the output values the system produces. The en- ronment cannot be assumed to be static or even e?ectively computable; for example, it may include humans or other real-world elements. Concurrency: In models of interaction, computation may be concurrent; a computing agent can compute in parallel with its environment and with other agents. The interaction paradigm provides a new conceptualization of compu- tional phenomena that emphasizes interaction rather than algorithms. C- current, distributed, reactive, embedded, component-oriented, agent-oriented andservice-orientedsystemsallexploitinteractionasafundamentalparadigm.