The theory of questionnaires is concerned with the elaboration of choice or decision models for the design of experiments of processes. Many different situations are covered by the theory. For example, making a series of clinical texts with a view to giving a medical diagnosis based on the combination of the various symptoms, asking a set of questions in order to chart some specific information needed when taking an administrative decision; running through a technical check-list prior to take of; choosing calls at the game of bridge; making provision for the various possible situations which may occur in a computer program.