2.6 Constituent Parts

In general, what are the parts of a system? The answer is not always obvious, as the “parts” of a program could be lines of code, variables or sub-programs. A system’s elemental parts are those not formed of other parts, e.g. a mechanic stripping a car stops at the bolt as an elemental part of that level. To decompose it further gives atoms which are physical not mechanical elements. Each level has a different elemental part: physics has quantum waves, information has bits, psychology has qualia and society has citizens (Table 2.1). Note that a qualia is a basic subjective experience, like the pain of a headache. Elemental parts then form into more complex parts, as for example bits form bytes.



Other parts



Friendships, groups, organizations, societies.



Cognitions, attitudes, beliefs, feelings, theories.



Bytes, records, files, commands, databases.


Quantum waves?

Quarks, electrons, nucleons, atoms, molecules.

Table 2.1:System elements by level

 A system’s constituent parts are those that interact to form the system but are not part of other parts (Esfeld, 1998), e.g. the body frame of a car is a constituent part because it is part of the car but not part of any other car part. So, dismantling a car entirely gives elemental parts, not constituent parts, e.g. a bolt on a wheel is not a constituent part if it is part of a wheel. To understand a system one must identify its constituent parts not only its elemental parts.

How elemental parts give constituent parts is the system structure, e.g. to say a body is composed of cells ignores its constituent structure: how parts combine into higher parts or sub-systems. Only in system heaps, like a pile of sand, are elemental parts also constituent parts. An advanced system like the body is not a heap because the cell elements combine to form sub-systems just as the elemental parts of a car do, e.g. a wheel as a car constituent has many sub-parts. Just sticking together arbitrary constituents in design without regard to their interaction has been called the Frankenstein effect (Tenner, 1997), as Dr. Frankenstein made a human being by putting together the best of each individual body part he could find in the graveyard – the result was a monster. The body’s constituent parts are for example, the digestive system, the respiratory system, etc., not the head, torso and limbs. The specialties of medicine often describe body constituents.

A general model of system design needs to specify the constituent parts of systems in general.