Structure of SystemStructure of System

Simulation & Modeling

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Some of the materials in this slide are my summary from Principle of System by Jay W. Forrester, Productivity, 1971

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Overview System

Structure Structure System Boundary

Classification of S stems Classification of Systems: Open System Feedback / Closed System Feedback / Closed System

Positive feedback system Negative feedback systemNegative feedback system

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Objective

By the end of this lesson you should be able to draw and define a systemable to draw and define a system

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1. System

Definition: System is a grouping of components or parts that operate together forcomponents or parts that operate together for a common purpose

A system is a part of some potential reality where we are concerned with space-time peffects and causal relationship among parts of the system

A system may include people as well as physical parts

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System as a black box

We define a system to be a closed world where we clearly separate items that arewhere we clearly separate items that are integral parts of the system from items that can affect the system from thethat can affect the system from the outside

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Example of System: Family

Family is a system for living and raising childrenchildren

Picture source: or.ucr.edu

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Example of System: Automobile

Automobile is a system of components that work together to providethat work together to provide transportation

Picture Source:

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Example of System: Warehouse

A warehouse and loading platform is a system for delivering goods into truckssystem for delivering goods into trucks

Picture Source: http://www.rrii.com/images/Arlington_Warehouse_Pic.gif

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Example of System: management

Management is a system of people for allocating resources and regulating theallocating resources and regulating the activity of business

Picture source: http://www.ingres.com/images/about/group-pic-management.jpg

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Example of System: Web

Web is an ecosystemS t ithi th b Systems within the web eBay Blogosphere Digg Flickr MySpace

Picture source: http://upload.wikimedia.org/wikipedia/commons/thumb/b/b9/WorldWideWebAroundWikipedia.png/800px-WorldWideWebAroundWikipedia.png

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Discussion & Exercise

Can you find other system?Wh t th t f th t ? What are the components of the system?

What is the purpose of the system?

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2. Structure

Definition: A structure is effective interelation and interpretation of ourinterelation and interpretation of our observation in any field of knowledge

Without an organizing structure, knowledge is mere collection ofknowledge is mere collection of observations, practices and conflicting incidents

Structure determines behaviour Structure determines behaviour

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Interacting Components

Any specified behavior of a system must be produced by a combination of thebe produced by a combination of the interacting components.

Those components lie within a boundary that defines and encloses the system

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Example of Structure: Physics

The law of Physics is a structure to interrelate our many observations aboutinterrelate our many observations about nature.

This structure of physical knowledge is the foundation of todays technology

Picture source: http://oz.irtc.org/ftp/pub/stills/1997-08-31/physics.jpg

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Example of Structure: System Management

Management system is a structure to unify the diverse manifestation ofunify the diverse manifestation of psychological, industrial and economic processesprocesses

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Causal Thinking

Causal thinking is the key to organizing ideasideas

Instead of cause, affect or influence can be used to describe the related components in the system

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Understand Cause & Effect Some are logical (e.g. physics)

Food intake weight Food intake weight Money happiness Fire smoke Fire smoke

Some are not (e.g. sociology, economics)( g gy, ) Use of seatbelts reduced highway

fatalities Shortened daylight hours increased

suicide rates

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3. System Boundary

Where is the boundary, that encompasses the smallest number ofencompasses the smallest number of components, within which the dynamic behavior under study is generated?behavior under study is generated?

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Self-contained system

Self-Contained System: nothing flow in and out of systemand out of system

Most system are not self-containedy They function in an environment that

affect their behavioraffect their behavior

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Difficulty in defining Boundary

1. Difficult to decide at what level the various sub systems should be detailedvarious sub systems should be detailed Subopmitization: decision that optimize

behavior of a sub system but that are lessbehavior of a sub system but that are less optimal for the system as a whole

2 Difficult because of interaction and 2. Difficult because of interaction and overlapping parts with other system3 Diffi lt t d fi th li k ith th 3. Difficult to define the linkage with the environment

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Closed System

In concept, a feedback system is a closed systemsystem.

Its dynamic behavior arises within its internal structure

Any interaction which is essential to the Any interaction which is essential to the behavior mode being investigated must be included inside the system boundarybe included inside the system boundary

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Building Blocks

Within the system boundary the basic building block is the feedback loopsbuilding block is the feedback loops.

Interconnection of feedback loops form a system

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4. Classification of System

System can be classified into O t Open system

Feedback (closed) system

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4a. Open System

An open system is one characterized by output that respond to inputs but whereoutput that respond to inputs but where the outputs are isolated from and have no influence on the inputno influence on the input

It is not aware of (observe and react to ) its own performance

d l f Its past action does not control future action

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Example of Open system: Watch

A watch, taken by itself, is an open system because it does not observe itssystem because it does not observe its own inccuracy and adjust itself

Picture source: http://www.37signals.com/svn/images/watch-panel.jpg

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Example of Open System: Car

A car is an open system which by itself is not governed by where it has gone in thenot governed by where it has gone in the past nor does it have a goal of where to go in the futurego in the future

Picture source: http://www.global-rental.comp g

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Discussion: open system

Can you find other open system?E l i h d thi k it i Explain why do you think it is an open system

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4b. Feedback System

It is also called Closed System

A feedback system has a closed loop structure that bring the results from past action of thethat bring the results from past action of the system back to control future action

Feedback system control action is influenced by the results of its own previous action or past behavior

Its past action control present and future action

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Feedback Loop Well conceived systems contain feedack loop.

Feedback involves monitoring the actual behavior of a system and comparing itsbehavior of a system and comparing its behavior to standards

Information about deviation from standard is transmitted to the appropriate point in thetransmitted to the appropriate point in the system so that effective action can be taken

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Category of Feedback System

There are two classes of feedback system:system: Positive feedback: growth

N ti f db k l ki Negative feedback: goal seeking

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4b1. Positive Feedback System

Positive feedback generates growthprocesses wherein action builds a resultsprocesses wherein action builds a results that generate still greater action

It is in the positive feedback form of system structure that one finds the forces of growth

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Example (+) Feedback System

Bacteria multiply to produce more bacteria which increase the rate at which new bacteriawhich increase the rate at which new bacteria are generated

Picture source: http://www.scharfphoto.com/fine_art_prints/archives/199812-053-Soil-Bacteria.jpg

In this positive feedback system the generation of new bacteria depends on the bacteria

Bacteria.jpg

of new bacteria depends on the bacteria accumulated from past growth of bacteria

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4b2. Negative Feedback System

Negative feedback system seeks a goal and responds as a consequence of failingand responds as a consequence of failing to achieve the goal

It is in the negative feedback, or goal seeking, structure of systems that one finds the causes of fluctuation and instability

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Example (-) Feedback System: AC

Air conditioning system of a house is controlled by a thermostat which reponds to the heat y ppreviously produced by the AC

Picture source: http://www.rd.com/images/tfhimport/2001/May01_Air_Conditioner_Clean/20010501_Air_Conditioner_Clean_page002img001_size2.jpg

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AC (cont)

Because the heat already produced by the system controls the forthcomingthe system controls the forthcoming generation of heat, the AC system represent a negative feedback that seeksrepresent a negative feedback that seeks the goal of proper temperature

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Example (-) Feedback System

A watch and its owner form a negative feedback system when the watch isfeedback system when the watch is compared with the correct time as a goal of proper time and is adjusted toof proper time and is adjusted to eliminate error

Picture source:http://www.geekologie.com/2007/12/10/imobile-watch-phone.jpg

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View Point

Whether a system should be classified as an open system or a feedback system is notopen system or a feedback system is not intrinsic to the particular assembly of parts but depend on the observers view point in defining p p gthe purpose of the system

You can always broaden the scope and purposeof the system to change from open to feedback system and from feedback to open system

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Review Classification of Systems

System:O t Open system: Past action does not control future action

Feedback or Close systems: Feedback or Close systems: Past action controls future action

Positive feedback loop Negative feedback loopg p

Depend on observers viewpoint

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Summary

You have learned in this lesson aboutS t thi ki System thinking

System definitionS System structure

System boundary

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Discussion & Exercise: System Structure

Please select any system that interesting for your groupfor your group

Can you draw the system structure? Specify the parts or components of

system as variables of the system Then draw arrow to connect the influence

of one part to the other partp p

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Discussion: Boundary

Define from your system:H th i bl i fl th i bl ? How the variables influence other variable?

Is it a closed or open system?C fi d f db k l ? Can you find some feedback loop?

Can you draw the system boundary (to make it l d t )?it a closed system)?

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Discussion Points

Define from your system: System boundary System boundary Is it open or feedback system? Variables in the system Variables in the system How the variable influence other variable Can you change viewpoint to form feedback Can you change viewpoint to form feedback

loops

Keep your discussion for next week

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Tips When there is a double arrow in the influence

line it indicates there are more variables insideline, it indicates there are more variables inside that have not been specified

Select variables that can be measured quantitatively (by any means)q y ( y y )

Influence should be able to be measured as Influence should be able to be measured as direct effect (increase or decrease). Indirect effect indicates lack of variables in between

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Tips Change level of details of some variables to

obtain feedback loop (change viewpoint)obtain feedback loop (change viewpoint)