The systems of interest to us

Copyright 2016 Graham Berrisford. One of about 300 papers at Last updated 10/03/2019 13:44


The universe is an ever-unfolding processes in which we perceive discrete entities.

If every one of those discrete entities is a system, the term has no useful meaning.

Systems architects should understand the properties that characterise a system.

Because if it can't be described as having the properties of a system, then it ain't a system, and it can’t be designed as a system.

This paper is only a preface to get us started.


Systems as abstractions. 1

The primacy of behaviour or dynamics. 3

System boundary, inputs and outputs. 3

The granularity of atomic system elements. 4

A system classification. 4

Footnote: more system concepts. 5


Systems as abstractions

For some, to understand systems thinking requires making a paradigm shift as radical as is needed to understand Darwin’s evolution theory.

In discussion, people often refer to a named entity as a system.

They point at a machine or a business (like IBM) and say "the system is that thing there".

But with no further description, that is vacuous to the point of being meaningless.

Because, as many thinkers have told us, a system is a particular a way of looking at the world.

And any substantial entity can be described as manifesting (instantiating, realising) countless different systems.


Ashby, Ackoff, Checkland and other systems thinkers emphasise that a system is one perspective of a reality.

They distinguish abstract systems from concrete systems.

An abstract system is a description of how some part of the word behaves, or should behave.

Any part of the world that conforms (well enough) to the abstract system may be called a concrete system.

You can test that real-world entity against what the abstract system predicts.


A system may be described by typifying:

·         Actors who play roles in activities

·         Activities that follow rules

·         Attributes (state variables) of the system or its parts.


Here are a few simple examples to get us started.


A solar system

·         Actors: planets.

·         Activities: orbit the sun.

·         State: the current condition and position of the planets.


A termite nest

·         Actors: termites

·         Activities: deposit materials, disperse a pheromone.

·         State: the structure of the nest, which grows as termites deposit material at peaks in the pheromone gradient and disperse the pheromone.


A prey-predator system

·         Actors: wolves and sheep

·         Activities: births and deaths of wolves and sheep.

·         Material state: the condition of the wolves and sheep at a moment in time.

·         Information state: wolf and sheep population numbers (grow and shrink in response to each other, and may settle in a stable cyclical pattern).


A tennis match

·         Actors: tennis players.

·         Activities: the motions of the ball and the players.

·         Material state: the condition of the court, the balls and the players at a moment in time.

·         Information state: the game, set and match scores (a structural side effect of players acting according to laws of the game.)


A circle calculator

·         Actors: an software component

·         Activities: calculate perimeter, calculate area.

·         Information state: an invariant, the value of pi.


The systems of most interest to us

A system is characterised by exhibiting behaviours that are regular or repeatable, orderly or rule-bound.

So, the conformance of actors’ behaviours to defined roles and rules can be assessed.

Of particular interest are social systems in which actors process information encoded in memories and messages that describe or direct reality.

Especially human social systems in which the information describes or directs some entities or events of importance to people.

And business systems in which some or all of the information is digitised.


The primacy of behaviour or dynamics

The first decision  is what to treat as the basic elements of the social system.

The sociological tradition suggests two alternatives: either persons or actions.” Seidl 2001.

Is a system a set of actors performing actions? Or a set of actions performed by actors?


Some see a system as a structure in which things (actors or other) are related to each other.

But that definition fits every substantial entity in the universe; and if every entity is a system the term has no value.

Also, things may be related only tenuously, by their relationship to something else.

Are the employees of IBM to be called a system purely because they are all employed by IBM?

Ashby urged us to recognise that IBM can realise countless different (even conflicting) systems.


Some system thinkers define a system in a way particularly suited their subject matter.

However, both Ashby and Forrester pitched their view of systems as a very general system theory.

And both see a system as defined by what it does – its behaviour or dynamics.


The systems of most interest to us

A system of the kind that may be described using cybernetics, soft systems and System Dynamics

·         In cybernetics, Ashby said the question is not so much "what is this system?" as ''what does it do?"

·         In soft systems, Churchman said “a thing is what it does”.

·         In System Dynamics, dynamics are the rules that incrementally change the system state.

System boundary, inputs and outputs

To describe a system is to separate it from its wider environment.

The describer has to decide where to draw the boundary.

The boundary can be physical (as is a solid structure in a liquid) or logical.


A system can be closed or open, meaning that inputs and outputs cross its boundary.

The boundary may be expanded or contracted at the whim of the describer.

Having identified external structures or behaviours that interact with a system, the boundary can be expanded to include them.

Thus, the ecology of the first system is definable as a wider system.


The table below adds inputs and outputs to the actors, activities and state.

And shows the similarities between systems as they are defined in five different sources.


Generic structure

Principia Cybernetica

Boulding’s social system

Checkland’s Soft System

Maturana’s biological entity

Wikipedia’s “system” entry (2016)


Interrelated parts

Individuals perform roles in

Components interact coherently in

Interacting components are transformed and destroyed

Related components perform


interact in processes to meet goals by

repeatable processes according to

activities to meet a purpose by

by a network of processes that form

processes that transform


maintaining system state and

remembered mental images, and

maintaining their integrity and

a machine, a concrete unity


I/O boundary

sending/receiving information

exchange messages

sending/receiving inputs and outputs


inputs into outputs (material, energy or data)


to/from each other and external actors


to/from each other and external actors

in space


The granularity of atomic system elements

The granularity of the atomic actors, activities and state variables in a system is whatever a describer chooses.

In discussion and observation of the stickleback mating ritual, the particulars of any one stickleback are ignored.

We necessarily ignore their internal structures and behaviours, give no thought to the complexity therein.


Whatever the level, fine or coarse-grained, we hide the internals of what is regarded as atomic.

·         In modelling the cardio-vascular system, we ignore the internal biochemistry of the cells.

·         In modelling a tennis match, we ignore the cardio-vascular systems of the players.

·         In modelling a nation’s economy, we ignore the internal operations of businesses that pay dividends to investors.

A system classification

Our main interest is in dynamic systems; however passive data structures also feature in what follows.

And note that dynamic systems can be natural or designed.


Discrete entity

Disorganised disorderly entity


organised, orderly, stable

Passive structure

does not act

Dynamic system

behaves an orderly or rule-bound way

Natural system


Designed system

described (e.g. symphony or software system)


e.g. solar system


e.g. tree, cat


e.g. bee hive,

hunting party

Closed system

e.g. System

Dynamics model

Open system

I/O exchange

across boundary


Footnote: more system concepts


Natural language (five sources)

This table shows system features found in three dictionaries (A, B and C) and two popular internet sources.









Wholeness (or holism)






parts cooperate in processes to act as a whole (rather than act in isolation).

Inter-related components






all parts are related directly or indirectly

Orderly or rule-bound behaviour






system processes are constrained, bound by the rules of physics, chemistry or man.

System boundary (or encapsulation) 






things inside the system are separable from things outside the system.

Input/output exchange across boundary






the system is open to and interacts with its environment


The table suggests this general definition.

·         A system is a whole composed of inter-related components that exhibit orderly or rule-bound behaviours.

·         It may be encapsulated by a boundary, across which inputs and outputs may be exchanged with entities in  the wider environment.


Classical cybernetics (Weiner, Ashby, Turing)

The properties of systems were generalised by system theorists before and without consideration of business or software systems .

“The same concepts and principles of organization underlie the different disciplines (physics, biology, technology, sociology, etc.), providing a basis for their unification.” Principia Cybernetica

Principia Cybernetica says this of a system:

real systems are open to, and interact with, their environments….”

“Systems theory focuses on the arrangement of and relations between the parts which connect them into a whole.”

“Systems concepts include: system-environment boundary, input, output, process, state, hierarchy, goal-directedness, and information.” Principia Cybernetica (Web)


Use the links below to find discussion of system concepts associated with cybernetics:

·         Encapsulation of structure and behaviour

·         Information feedback loops

·         The primacy of behaviour


General system theory (Bertalanffy, Boulding, Rappaport)

To generalise from the analysis above, the general elements of a system might be expressed as

·         parts/actors (active structure) interact by

·         playing roles in processes (behaviours) to meet goals by

·         maintaining system state and

·         sending/receiving information to/from each other and

·         to/from the external environment (across the I/O boundary)

·         using resources.


Use the links below to find discussion of further concepts associated with general system theory:

·         Determinism and hysteresis

·         Holism and emergent properties

·         Complexity

·         Goal-directedness


System Dynamics (Forrester, Meadows)

Use the links below to find discussion of further concepts associated with system dynamics:

·         Chaos and non-linear behaviour

·         Unpredictability


Soft systems (Churchman, Checkland, Ackoff)

Churchman was concerned with business systems in particular.

He said "a thing is what it does" and outlined these considerations for a system.

·         the total system objectives and performance measures;

·         the system’s environment: the fixed constraints;

·         the resources of the system;

·         the components of the system,

·         their activities, goals and measures of performance; and,

·         the management of the system.




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