PREFACE: System theory for enterprise and business architects

“The most important work on EA and applied System Theory today.”  “Makes EA more powerful, coherent and usable.”


What theory underpins enterprise and business architecture methods and modelling languages?

It seems clear to me that the answer is general systems theory, which emerged from an interdisciplinary study of systems.


The goal of the early system theorists was/is to discover/define patterns and principles common to systems in every field of research, at every level of nesting.

General systems theory is about broadly applicable concepts and principles, rather than concepts and principles applicable to one domain of knowledge.

E.g. A system can be characterised as parts that interact in regular, repeated or repeatable behaviors.


The term general system theory was coined by Ludwig von Bertalanffy in the middle of the 20th century.

His ideas were picked by others including William Ross Ashby, Anatol Rapoport and others.

They worked in the fields of mathematics, psychology, biology, game theory and social network analysis.


An early focus of general system theory was on self-regulating systems such as the physiological systems of the body.

Such a homeostatic system (natural or designed) maintains itself in a stable or viable state through input/output feedback loops. 

This branch of system theory is sometimes called cybernetics.


A system may be defined in general as a set of interrelated or interacting elements.

This definition accommodates passive structures such as a necklace, or the Dewey Decimal System.

However, most system theorists focus on activity systems in which structures/components interact in behaviors/processes.


·         A living organism is a set of organs, muscles etc. that interact in processes to sustain the organism.

·         A cell is a set of organelles that interact in processes to sustain both the cell and the wider organism.

·         A business organization is a set of people and machines that interact in processes to achieve business goals.


For some, '''systems thinking''' is the cognitive process of studying and understanding systems of any kind - as above.

For others, the focus is on social organizations in particular.

Sociological systems thinking started in the 19th century.

In retrospect, this may now be seen as a specialism (of general system theory) that is focused on social and business organizations.

Background to this work

When a student of biology, then psychology, then software design, I picked up a few ideas that have stuck with me ever since.

Biology: a living entity is sensitive to changes in the state of its environment, and responds to them.

Psychology: a brain holds a model of things in its external environment.

System theory: an activity system is bounded by inputs and outputs from/to its external environment.

Michael A Jackson taught me that a software system holds a model of what it monitors and directs in its external environment.


These ideas have appeared and reappeared throughout a career in the fields of software, business and enterprise architecture.

But it wasn’t until 2011 that a systems thinker impelled me to document my thoughts.

He complained he could find not any theory underpinning enterprise architecture other than the Zachman Framework.

I was surprised he didn’t recognise that general system theory underpins enterprise architecture.

Setting off to document an explanation for him forced me (unexpectedly) to answer various questions mentioned below.

I hope you’ll find the journey to form coherent and consistent answers as interesting as I have done.

Questions to be addressed

This work draws on various theories to explain and discuss what a system is.

It looks at systems through the lenses of the scientific method, type theory and the philosophy most compatible with them.

It introduces a description theory based on the perspective of an evolutionary biologist.

It shows where system theory is applied in enterprise and business architecture methods and modelling languages.


Set and type theory

Some see a system as “set” of entities that interact, directly or indirectly.

Some see a system as a description composed of abstract types that are instantiated in working systems.

Q) How do mathematical set and type theories relate to system description?


Description theory

A system can exist in two forms - which may be called “abstract” and “concrete”.

A concrete system realises (or instantiates) an abstraction system description (or type).

Abstract system description

The Dewey Decimal System

“Solar system”

Laws of tennis

Defined roles (e.g. Orchestral parts)

The score of a symphony

Concrete system realisation

Books sorted on library shelves

Planets in orbits

A tennis match

Actors (e.g. Orchestra members)

A performance of that symphony


An abstract system describes a concrete system.

Q) What theory do we have for how to describe something?


Information theory

Some see a system as a collection of actors that interact by the exchange of information.

Q) How does information theory apply in system description?


Sociology, business and software

Business systems are often described in terms of inputs, transformational processes and outputs.

The inputs and outputs form a feedback loop with the wider environment.

Some see a system as a collection of human actors who interact in a social group to a common goal.

Q) What principles can be applied equally to social, business and software systems?