Page 160 - DCAP405_SOFTWARE_ENGINEERING

Unit 9: System Engineering

Notes
Figure 9.10: Types of Systems

Table 9.1: Four Types of Systems
Types of System Model Parts Whole Example
Mechanistic No choice No choice Machines
Animate No choice Choice Persons
Social Choice Choice Corporations
Ecological Choice No Choice Nature

These type form a hierarchy with ecological systems – the highest type. All but mechanistic
systems can incorporate as parts other systems of the same or a lower type, but not of a higher
type; for example, social systems (e.g., society) may incorporate animate systems (people) and
mechanistic systems (machines), but a mechanistic system cannot incorporate either an animate
or social system. Ecological systems can incorporate systems of all the other types.

Only animate and social systems can be said to be purposeful.
Now consider each type of system in a bit more detail.
1. Mechanistic Systems: Mechanistic systems and their parts have no purposes of their own,
but their essential parts make possible the functioning of the whole. All mechanisms are
mechanistic systems. Plants are also. Clocks are common examples of such systems; they
operate with a regularity dictated by their internal structure and the causal laws of nature.
Neither the whole nor the parts of a clock display choice, but they have functions. Similarly,
an automobile is a mechanical system that has no purpose of its own but serves its driver’s
and passengers’ purposes. In addition, an automobile’s fuel pump (a mechanical system)
has the function of supplying its fuel injector or carburetor with fuel, without which the
automobile could not carry out its defining function.
Mechanistic systems are either open or closed, closed if their behavior is unaffected by any
external conditions or events; open if they are so affected. The universe was conceptualized
by Newton as a closed (self-contained) mechanical system, with no environment-like a
hermetically sealed clock. On the other hand, the planet Earth is seen as an open system,
one whose motion is influenced by other bodies in the solar system.

2. Animate Systems: These are conceptualized as purposeful systems whose parts have no
purposes of their own. The principal purpose of such systems is survival. A person’s lungs
have no purpose of their own; but they function to enable a person to extract oxygen from
the environment so as to survive. Animate systems are necessarily open; they must interact

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