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10.1 Complex systems 269

Property Description

Volume The volume of a system (the total space occupied) varies depending on how the
component assemblies are arranged and connected.

Reliability System reliability depends on component reliability but unexpected interactions can cause
new types of failures and therefore affect the reliability of the system.
Security The security of the system (its ability to resist attack) is a complex property that cannot be
easily measured. Attacks may be devised that were not anticipated by the system designers
and so may defeat built-in safeguards.

Repairability This property reflects how easy it is to fix a problem with the system once it has been
discovered. It depends on being able to diagnose the problem, access the components that
are faulty, and modify or replace these components.

Usability This property reflects how easy it is to use the system. It depends on the technical system
components, its operators, and its operating environment.

To help understand the effects of systems on organizations, various methodologies
Figure 10.2
Examples of have been developed, such as Mumford’s sociotechnics (1989) and Checkland’s Soft
emergent properties Systems Methodology (1981; Checkland and Scholes, 1990). There have also been
sociological studies of the effects of computer-based systems on work (Ackroyd
et al., 1992; Anderson et al., 1989; Suchman, 1987).

10.1.1 Emergent system properties

The complex relationships between the components in a system mean that a system
is more than simply the sum of its parts. It has properties that are properties of the
system as a whole. These ‘emergent properties’ (Checkland, 1981) cannot be attrib-
uted to any specific part of the system. Rather, they only emerge once the system
components have been integrated. Some of these properties, such as weight, can be
derived directly from the comparable properties of subsystems. More often, how-
ever, they result from complex subsystem interrelationships. The system property
cannot be calculated directly from the properties of the individual system compo-
nents. Examples of some emergent properties are shown in Figure 10.2.
There are two types of emergent properties:

1. Functional emergent properties when the purpose of a system only emerges
after its components are integrated. For example, a bicycle has the functional
property of being a transportation device once it has been assembled from its
components.
2. Non-functional emergent properties, which relate to the behavior of the system
in its operational environment. Reliability, performance, safety, and security are
examples of emergent properties. These are critical for computer-based systems,
as failure to achieve a minimum defined level in these properties usually makes