Post on 17-Oct-2014
description
Introduction to Systems Thinking: System Structures and Behaviour
Sydney Limited WIP SocietyJason Yip
j.c.yip@computer.orghttp://jchyip.blogspot.com
@jchyip
Select a problem as a working example. It should be somewhat complicated, and not too simple.
What is a system?
A system is a set of things interconnected in such a way that they produce their own pattern of behaviour over time
A system is more than the sum of its parts
http://mennodiscuss.com/viewtopic.php?f=6&t=16392#p456262
Systems consists of three things
1. Elements2. Interconnections3. Function (non-human system) or Purpose
(human system)
Examples of systems
● Digestive system● Sports team● School● City● Factory● Corporation● National Economy
● Animal● Tree● Forest● Earth● Solar system● Galaxy● IT system
Systems mostly cause their own behaviour; outside events unleash that behaviour
Do politicians cause recessions and booms? Or is it inherent to market economies?
Do competitors cause companies to lose market share? Or do their own policies create losses that competitors exploit?
“Every system is perfectly designed to achieve the results it gets.”
Dr. Don Berwick
Describe your situation as a system
● What are the elements?● What are the interconnections between the
elements?● What is the purpose of the system?
Intended vs actual based on behaviour?
Stocks and Flows
Stocks are the elements you can see, feel, count, or measure at any given time
Examples of Stocks
● Water in a bathtub● A population● Books in a book store● Wood in a tree● Money in a bank
Stocks change over time via Flows
● Work flow● Information flow● Both inflow and outflow
http://lssacademy.com/2008/02/24/lets-create-a-current-state-value-stream-map/
Information Flow
Work Flow
Stocks
https://flic.kr/p/9az8q1
Inflow
Outflow
Information flow
Stock
Stocks provide a memory of flows
Stocks act as “shock absorbers”
Stocks introduce delay.
It takes time for flows to affect stocks.
Delays decouple inflow and outflow
Examples of stocks decoupling flows
● Gasoline storage tanks● Wood in a forest● Water reservoir
“Stocks are pretty much queues”
Me
Let’s try describing a typical Agile team using stocks and flows
How might stocks and flows change how you describe your situation?
Feedback loops
Systems run themselves via feedback loops
Balancing feedback loops
● Thermostat● Guided missile● Iterative, incremental software development
A stock with two competing balancing loops
How feedback fails
● Late, lost, unclear, incomplete, hard to interpret information
● Weak, delayed, resource-constrained, ineffective response
Two competing balancing loops with delays
The problem with forecast-driven supply chains
A delay in a balancing feedback loop makes a system likely to oscillate
Aside: This is generally solved by using kanban
Reinforcing feedback loops
● Market collapse: uncertainty -> remove money -> more uncertainty
● Compound interest● Death march: Too much to do -> work
harder -> more bugs -> work even harder
A stock with one reinforcing loop and one balancing loop
If A causes B, is it possible that B also causes A?
How might feedback loops change how you describe your situation?
Dealing with systems
Systems consists of three things
1. Elements2. Interconnections3. Function (non-human system) or Purpose
(human system)
Changing elements usually has the least effect; changing interconnections or purpose is usually more dramatic
Examples
● Change all members of a sports team vs change rules of the game or the definition of winning
● Change people in the organisation vs change the way of working or the definition of organisational success
Focus more on interconnections and interactions than elements
● Interaction flow / sequence over class structure
● Work flow / value stream over org structure
System interactions operate through information flow
Address incongruent purposes
System purposes do not necessarily match the intention of the designers or actors within it
How might you intervene in your situation to improve the system?