Motivating the Behavioral Approach

Modelling and Control of physical systems are well developed branches of Systems and Control Theory and Control Engineering. Traditionally, these branches of human knowledge have been developed within a paradigmatic perspective of input/output thinking: the way an abstraction is obtained from the physical entity involves the notions of input and output variables, and the ideas of cause and effect. This process is informally referred to as modelling. In this chapter our aim is to reconsider the input/output paradigm in modelling by studying some fundamental questions concerning the modelling of physical systems. After doing this, we hope to understand better why the traditional way of modelling and control of systems may not be the best one. We propose to use ideas from the Behavioral Approach to Systems and Control. This approach does not wish to neglect or forget the paradigmatic input/output approach; rather it offers new possibilities.