Encapsulation of system structure and behaviour

Copyright 2017 Graham Berrisford.

One of about 300 papers at http://avancier.website. Last updated 21/02/2017 17:14

System concepts

“Systems concepts include: system-environment boundary, input, output, process, state….”     Principia Cybernetica

This table arranges these concepts in a generic structure.

 

General System Theory

A bounded structure of

actors/organs interact by playing

roles in

processes to meet

goals, by maintaining

system state and exchanging

inputs/outputs with each other and with

entities outside the boundary, using

system resources.                                    

 

The environment outside a system’s boundary contains structures/entities and behaviors/events that can change the state of the system, or be changed by the system.

“Every living organism is essentially an open system. It maintains itself in a continuous inflow and outflow…” Bertalanffy

TOGAF regards a business as a system that maintains itself in a continuous inflow from suppliers and outflow to customers.

System encapsulation (IPO) as system scoping

There are usually feedback loops between a system and its environment.

To encapsulate a system means defining its input-process-output (IPO) boundary.

The inputs and outputs can be flows of information, material or energy.

TOGAF defines a business and each application/technology component it uses by the I/O services it offers.

 

“Any suggestion that we should study "all" the facts is unrealistic, and actually the attempt is never made.

What is necessary is that we should pick out and study the facts that are relevant to some main interest that is already given.” Ashby

A system describer defines the inputs and outputs with reference to an already-given interest or aim.

 

In thermodynamics, the inputs and outputs are matter and energy.

An open system exchanges energy and matter with its environment.

A closed system exchanges energy, but not matter, with its environment.

 

In cybernetics, the primary inputs and outputs are materials and information.

“In this discussion, questions of energy play almost no part; the energy is simply taken for granted.” Ashby

 

In social, business and software systems, the primary inputs and outputs are information or data flows.

“EA is about “information intensive organisations”, ArchiMate 2.1

 

closely connected with system theory is… communication.

The general notion in communication theory is that of information.

A second central concept of the theory of communication and control is that of feedback.” Bertalanffy

System design as a process

SIPOC is an acronym that captures GST ideas used in business systems analysis, design, process and quality improvement.

The conventional design process defines the system-environment boundary thus:

-1- Define Customers - entities in the environment that need outputs to meet their goals

-2- Design Outputs - that customers need from the system

-3- Design Inputs – that the system needs to produce the outputs

-4- Define Suppliers - entities in the environment that will supply the inputs

-5- Design Processes - to produce the outputs from the inputs.

 

To which one might reasonably add:

-6- Define Roles - in which actors can perform the process steps

-7- Hire and/or make Actors - to play the roles

-8- Organise, deploy, motivate and manage the actors – to perform the processes.

 

Of course, the process is iterative in practice.

Systems and processes can be, and are, composed and decomposed.

Decomposition continues until individual actors can be hired or made to perform the required behaviors.

 

At every level of composition, a describer defines cross-boundary input/output flows.

If you expand the system-environment boundary then external events become internal events that pass between subsystems.

If you contract the system-environment boundary then internal events become external events, crossing that boundary.

 

The system-environment boundary is a choice made by system describer(s).

It meaningless to point to an entity (say IBM) and call it a system.

Because it isn’t a system until those in the discussion agree on its boundary and which of its properties are relevant to some interest already given.

Encapsulation in EA

“Every living organism is essentially an open system. It maintains itself in a continuous inflow and outflow…” Bertalanffy

TOGAF regards a business as a system that maintains itself in a continuous inflow from suppliers and outflow to customers.

 

General System Theory

In EA/TOGAF terms

A bounded structure of

A bounded organisation of

actors/organs interact by playing

actors/components interact by playing

roles in

roles in

behaviors to meet

processes to meet

goals, by maintaining

goals/objectives/requirements by maintaining

system state and exchanging

data entities and providing

inputs/outputs with each other and with

input/output services to each other and to

entities outside the boundary, using

entities outside the boundary, using

system resources.

platform technology components.

 

EA is concerned with coupling not only of the enterprise system to its environment, but of subsystems to each other.

It takes the holistic view; it looks to integrate subsystems to the benefit of the wider business system.

 

Enterprise architects encapsulate whole systems and internal actors/components - to describe their roles at an abstract level.

Encapsulated actors/components interact with each other and with external entities via input and output feedback loops.

Each system/actor/component can be seen as an input-process-output mechanism.

It receives messages about the state or needs of entities in its environment

It processes information in the light of the current state of the business and/or environment.

It sends messages to help actors produce desired effects or outcomes.

 

 

All free-to-read materials at http://avancier.website are paid for out of income from Avancier’s training courses and methods licences.

If you find the web site helpful, please spread the word and link to avancier.website in whichever social media you use.