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.
|
Level |
Element |
Other parts |
|
Community |
Citizen |
Friendships, groups, organizations, societies. |
|
Personal |
Qualia |
Cognitions, attitudes, beliefs, feelings, theories. |
|
Informational |
Bit |
Bytes, records, files, commands, databases. |
|
Physical |
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.