Boundaries: input-output
The system boundaries are usually the input-output relationships which can be observed. The system to be examined is the process between the input and the output. At first, this process is a “black box” which is described by the two boundary-specific groups and it is from here, from this relation that the characteristics of the process must be derived.
Just consider how long it took for humanity to map the processes of the human body; even as great a thinker as Aristotle thought that the heart was the seat of thinking. It is interesting to have a look at how our views about the process of blood circulation evolved until Harvey in the 17th century and how Indian, Arabic and European scholars were in a dither about the relationship between breathing, veins, arteries, heart valves and heart rate in the medieval age.
A basic computational task of system science is to model the process of the system on the basis of input-output measurements and the relationships observed. This task is called system identification. The figure shows the input, the output, the various processing operations taking place in between, and the mysterious black box related to the questions.
Naturally, it is essential to gain a deep understanding of the examined system and how it works. Once we have described the behaviour of the system with mathematical equations, the system becomes more like a “grey box” whose structure is clear to us, so we can move on to identify its parameters.