System properties: an introduction
Copyright 2016 Graham Berrisford.
One of about 300 papers at http://avancier.website. Last updated
22/08/2017 23:00
The universe and human existence are ever-unfolding processes
in which we perceive discrete entities.
Some entities are called systems, but what makes an
entity a system?
System operators don't have to understand the properties that define what a system is.
Just as a footballer doesn't have to understand how kicking a football could be described using aerodynamics theory.
But systems describers have to understand the properties that define what a system is.
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.
Contents
Generalising
from dictionary definitions
Generalising
about activity systems
Sequences in
system operation and in system design
This table shows system features found in the two popular internet sources and three dictionaries (A, B and C)
|
Feature |
Google |
W’pedia |
Meaning |
|||
|
Wholeness (or
holism) |
yes |
yes |
yes |
yes |
yes |
parts cooperate in processes to act as a whole (rather than act in isolation). |
|
Inter-related
components |
yes |
yes |
yes |
yes |
yes |
all parts are related directly or indirectly |
|
Orderly or
rule-bound behaviour |
yes |
yes |
|
yes |
yes |
system processes are constrained, bound by the rules of physics, chemistry or man. |
|
System boundary (or
encapsulation) |
|
|
yes |
yes |
yes |
things inside the system are separable from things outside the system. |
|
Input/output
exchange across boundary |
|
|
yes |
yes |
yes |
the system is open to and interacts with its environment |
The systems
of interest here are characterised by orderly or rule-bound behavior.
All such
systems are islands of stability carved by humans or by evolution out of the
ever-unfolding processes of the universe.
Every system
has a limited life time; some change in discrete evolutionary steps from one
generation to the next.
A system
classification based on system properties above
This table maps system properties, drawn from dictionaries above, to a classification of system types.
Most of this work is about dynamic activity systems.
|
A system
classification |
||||
|
Discrete entity |
Entity that cannot be described as a system, because it is disorganised, unstable or continually changing |
|||
|
Entity that can be described as a system System boundary Wholeness Inter-related
components |
A passive structure that is stable but has no behaviour |
|||
|
Dynamic activity
system Orderly or rule-bound behaviour |
Naturally-evolved
system does not depend on
description by actors |
Inorganic natural machine (e.g. solar system) |
||
|
Organic entity (e.g. tree or cat) |
||||
|
Natural social organisation (e.g. bee hive, hunting party) |
||||
|
Designed system depends on description by actors (symphony, business or
software system) |
Closed system (can be modelled using System Dynamics) |
|||
|
Open system Input/output exchange across boundary |
||||
To call something a system without reference to testable
considerations is to say little.
Churchman says "a thing is what it does" and outlines five 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.
But those are considerations for business organisations in particular.
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)
This table presents an analysis of concepts from five sources.
|
Generic structure |
Principia Cybernetica |
Boulding’s social system |
Checkland’s Soft System |
Maturana’s biological entity |
Wikipedia’s
“system” entry |
|
Active structure |
Interrelated parts/actors |
Individuals perform roles in |
Components interact coherently in |
Interacting components are transformed and destroyed |
Related components perform |
|
Behavior |
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 |
|
State |
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) |
|
Environment |
to/from each other and external actors |
|
to/from each other and external actors |
in space |
|
To generalise from the above analysis, a set of basic considerations would be:
· parts/actors (active structure) interact by
· playing roles in processes (behaviors) 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.
At the risk of being simplistic, a business system operation
works as in the left hand column of the table below.
And a natural system design method is to (roughly) reverse the run-time sequence - as in the right hand column of the table below.
After implementation, run-time actors should behave in
reality as the design-time description directs them to behave.
|
A
sequence in run-time reality |
A
sequence for design-time description |
|
|
1 |
Input events/messages trigger… |
Goals - desired outcomes |
|
2 |
Actors to perform activities in rule-driven… |
Outputs to enable the goals to be met |
|
3 |
Processes, that consume inputs and use resources to make… |
Inputs and resources needed to make the outputs |
|
4 |
Outputs, and so enable the consumers of those outputs to realise the… |
Processes/rules to transform inputs into outputs
using resources |
|
5 |
Goals, the desired outcomes, of the system sponsors. |
Actors to perform the processes |
|
6 |
Resources needed
by actors to do the work |
System properties discussed in the literature and on web site include:
· Encapsulation of structure and behaviour
· Change: adaptation and evolution
· Holism and emergent properties
· Chaos and non-linear behaviour
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