B107 Principles of Information Systems
TOPIC 4
WHAT IS A SYSTEM?
Objectives:
 To introduce some fundamental systems concepts

To look in detail at the nature of a system, and identify its 8 components.

To model systems generally in order to see their elements and the relationships between them.

To study the interaction between a system and its environment and how that interaction needs to
be controlled.
 To look at a subsystem as a system within an environment of other subsystems.

To classify systems according to their content and their structure.
Reading:


Ahituv et al (1994) Chpt 4
Beekman et al (1999) Chpt 12 pp 313-318 (not in reader)
Abstract Models of Aspects of Reality
People constantly try to make sense of their world: perceiving problems and trying to understand
them. Our perceived world is largely constructed in our own minds using various concepts and our
experiences.
Part of the IS professional’s role is in making models of the perceived problem situation.
Models are always a simplification of the situation: never the real thing. Their value is in clarifying
problems as a step towards solving them.
Problems in a Wider Context
Considering a problem too narrowly, or isolated from the context in which it exists can cause further
and more complex problems.
e.g.
 Building more cars to get from A-B necessitates more pollution.
 Fridges help keep foods fresh but release gases that deplete the ozone layer, causing global
warming .
These issues were not considered in addressing the immediate problems.
We must therefore ensure that in making a model, or some other representation of a perceived
problem, we are not blinded to the wider issues. This is where systems thinking provides helpful
concepts.
Other aspects of ‘blindness’ come from narrow specialisation in a single discipline. It is not nature that
carves the world into physics, biology, mechanical engineering, but humans. These disciplines can
become filters that impose a particular way of looking at things but exclude others.
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Reductionism versus Holism
Western science has until recently emphasised the reductionist approach: dividing or analysing
complex things into smaller things that are more manageable, rather like top down programming.
This assumes that the whole is only the sum of the parts, which may be true in some cases.
The systems approach takes the opposite view and looks at the behaviour of the system as a whole
and describes things in terms of boundaries, environments, hierarchy, equilibrium, feedback,
adaptation, openness vs closedness.
Systems thinking is a metadiscipline and tries to view things as wholes. It thus complements the
specialist views of particular analytic (reductionist) disciplines.
Definitions of a system
A system can be regarded as:
“A set of connected components considered to form a meaningful whole”
The verb ‘considered’ implies a perceiver, thus systems exist in a person’s mind, not necessarily in
the wider world.
Components are generally linked to some others, but not usually to all others. However altering one
component may alter the effect of the whole system.
Tuning the car engine may improve the car’s speed, adding a user may slow down the network.
Think of an example of:
1. A biological system:
2. A constructed system:
Constructed Systems
A definition of constructed systems is:
"A system is an assembly of components, connected together in an organised way. The components are
affected by being in the system and the behaviour of the system is changed if they leave it. This
organised assembly does something and has been identified as a particular interest." (Walker, p 10)
Thus, a system is a set of parts or elements, physical or abstract. Components are related to each other.
In a constructed system, these relationships need to be planned.
The components of the system and the relationships between them determine how the system works.
Components are affected by being in the system because of the synergy of the system, and the
components affect the system and change the system if they leave it.
Constructed systems are set up to achieve a set of objectives or goals. Planning of a system must
start from the goals, then identify the tasks which will achieve the goals. Good systems are those that
reach their goals.
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Characteristics of a System
A constructed system has 8 characteristics:
 Goals (short term) and a purpose (long term) Systems should be both effective (does it achieve
the goal/purpose) and efficient (does it do so in the best way)
 Inputs - from environment to system.
 Outputs - from system to environment.
 Boundaries - define and delineate a system. The system within the boundary should be selfcontained and controllable within those boundaries. But boundaries may be hard to define - see
Fig 4.2 p88 Ahituv et al.
 Environment outside the boundaries, with inputs and outputs interfacing between system and
environment.
 Components and Subsystems - these transform inputs into outputs. Components are the basic
elements, subsystems are systems themselves composed of components.
 Interrelations - between subsystems is the system structure. We use decomposition to identify
subsystems & their interrelationships.
 Constraints - imposed by the environment.
Example
Think of a fast food restaurant as a system. Identify examples of each of the 8 components.
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A Systems Approach to Problem Solving
The systems approach to a problem involves two stages:
 Expanding stage - reducing the level of complexity by identifying subsystems, components and
their interrelationships;
 Contracting stage - organising and integrating components into a new system, adding new ones
and deleting old as needed.
This is what we do when investigating the need for an information system.
We define the problem, including boundaries (expanding), then construct alternative solutions
(contracting)
See table 4.1 page 81 of Ahituv et al.
Structure of a system
When analysing and designing complex and/or large systems they need to be broken down until the
subsystems are manageable. This is called factoring and usually leads to hierarchies (fig 4.3 p.90).

Each subsystem has a function that contributes to the overall goal of the system:
 Subsystems may consist of subsystems.

How a system is divided into meaningful subsystems (factoring) is a matter of system design and
implementation and will vary with the perspective of the designers.

A subsystem's environment is the system with all its subsystems. The subsystem will interact
with this environment.

The strongest interactions must be those within the subsystem, not those between subsystems.
Interactions between subsystems
Each partitioned subsystem has inputs, outputs and interacts with other subsystems. The more
interactions in a system, the more complicated the analysis of the system.
Interaction between subsystems is called coupling.
Coupling is of 3 sorts (see fig 4.4 p.92):
 Output of one subsystem is input to another
 Common resources between subsystems
 Common environment
Generally, the amount of coupling should be low and it is necessary to structure this in the design of
the system.
A variety of strategies aim to reduce the inputs and outputs shared between subsystems.
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Reducing and Controlling Interaction

Group closely interacting activities together.

Exception principle - subsystem is independent in normal functioning, but interactions occur for
exceptions (e.g. reports to managers if under target).

Cluster subsystems using a single interface (fig 4.5 p. 93).

Decouple (loosen the connections) to allow subsystems to operate as independently as
possible…methods include buffering, flexible resourcing (slack resources), standardisation (fig 4.6
p. 94)
 Buffering allows inputs to be stored until the subsystem can deal with them.
 Slack resources within a system allow inputs to be dealt with immediately.
 Standards for dealing with inputs from outside help to reduce disruption.
Some 'interrupts' simply can't be helped. Ways must be structured for these to be dealt with and still
allow the subsystem to carry on with its own processing afterwards.
The system trinity
Churchman's definition of a human designed system (pp 94 -97) identifies 3 core roles for a system to
be successful:

User - who needs a high performance system;

Decision maker - who allocates resources to the system;

Designer - who specifies the system to maximise its utility for the user.
In information systems development these roles may be combined (see later Topics):

End user developers (for small and/or simple systems)

Participative system development methodologies
Classifying systems
Systems can be classified in a number of different ways. Ahituv gives one categorisation (pp. 99 102)

Natural v human construction;

Abstract v concrete (physical or social);

Closed v open;

Deterministic (predictable), probabilistic (some risk) or random (unpredictable);

Human, Machine, Human/machine (socio-technical);

Adaptive/nonadaptive;

Simple/Complex;

Open loop/ Closed loop - An open loop system has no component performing a system control.
Closed loop systems contain at least one component that provides a system control function.
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Example
Classify an information system according to this categorisation:
 Natural or human construction?

Abstract or concrete?

Closed or open?

Deterministic or probabilistic or random?

Human or Machine or Human/machine

Adaptive or nonadaptive?

Simple or Complex?

Open loop or Closed loop?
Control and Feedback
Open Systems exchange information materials and energy with the environment.
An additional feature of open systems is the ability to adapt (ie adjust) to environmental change to
continue its existence and achieve its goals.
FEEDBACK is used to control the necessary adjustments.
Feedback can be defined as input used to regulate the system in accordance with its goal or purpose.
A system will generally have a control mechanism that monitors the transformation process to
ensure that outputs meet the goals of the system.
Control has three stages:
 Establish the goals of the system.
 Measure outputs against those goals
 Make corrections to system processing if outputs do not measure up to the goals.
The feedback loop
A closed-loop system contains subsystems that are linked by a feedback loop (Fig 4.8 Ahituv). These
are the controlled subsystem and the control subsystem.

Information from the output is available to the control subsystem that compares the feedback
signals to the goals of the system.

When it is necessary, the control subsystem directs signals to the input element to change the
operations of the system in order to bring the outputs into line with the goals.
 When the system is performing well, it generates positive feedback and the control mechanism
signals the system to maintain the current course.
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One more classification of types of systems
Checkland classifies systems into 5 types:
Natural Systems
Designed Abstract
Systems
e.g. the law
Designed Physical
Systems
Human Activity
Systems
e.g. the theatre
and ? transcendental systems – which are beyond knowledge
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