Any description of the workings of nature by means of measurements and ob­ servations is beset with the problem of how to cope with an immense amount of information. In physics, it is an established approach to derive basic equations which then serve as cornerstones of what is called a theory of the phenomena. This derivation is based on certain characteristics of the phenomena, the refine­ ment of which results from a reduction of the amount of empirical information, with the reduction leading to an enhancement of the very characteristics that are sought for in the otherwise seemingly amorphous wealth of data. If physics is mainly concerned with the derivation of equations, lately there has emerged a conceptually different approach, which in a way is equivalent to a reversal of the line of attack: here, the basic equations serve as the point of departure and the aim is to demonstrate that the equations are capable of de­ to represent the essence of the scribing certain characteristics which are thought phenomenon under investigation. By definition, this variant approach must tran­ scend the realm of pure physics and could possibly be termed "applied mathe­ matics" in a broader sense. The phenomena it strives to characterize arise from a range of influences such that a combination of theoretical concepts from physics, chemistry, engineering, biology, etc. , is called for.