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Flashcards in Systems Theory Deck (22)
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1

Define Systems Theory (in an organisational context)

A powerful means of analysing and improving business processes (systems), identifying system behaviour, and what/whom needs to be controlled.

By modelling the world around us we can start to reason about the behaviour of systems

2

Reductionism/Analysis and Synthesis

Reductionism/Analysis
— focus on components
— describes the system just by the sum of its parts (excludes interconnectivity)
— hence, is only good for low interdependency, low interconnectivity

Synthesis
— includes the interconnectivity (holistic)
— good for high interdependency (social constructions, ecosystems, computer networks, etc.)

3

7 system characteristics

1. interrelated components working towards a collective goal
2. interconnected (no complete isolation)
3. can be complex — (sub-systems, supra-systems)
4. sub-systems interact by exchanging information via well-defined interfaces
5. linkage or coupling between systems varies
6. transform inputs into outputs (the system's function)
7. emergent properties

4

tight and loose coupling

tightly coupled — strong interdependencies (e.g. machinery)

loosely coupled — more independent, less reliance on other components (e.g. postal service)

5

5 system components

1. Input
2. Transformation process
3. Output
4. Feedback mechanism (sensor)
5. Control mechanism

6

More and more technical systems arise because ...

(A) cheapening, more capable sensors and
(B) increasing ability to network things (Internet, faster computation)

7

What is the STAMP method and why is it useful

Systems Theoretic Accident Model and Processes

• Nowadays, many systems are socio-technical, where many errors occur on both sides.
• An accident or loss is very rarely caused by a single error or failure.
• Systems theory can help us identify what or whom needs to be controlled.

A useful way to analyze accidents, particularly system accidents. In STAMP, systems are viewed as interrelated components that are kept in a state of dynamic equilibrium by feedback loops of information and control.

8

positive and negative feedback

Positive feedback
• self-reinforcing feedback
• unsustainable (e.g. mass-panic)

Negative feedback
• The act of reversing the discrepancy between desired and actual output. (e.g. central heating system)
• Delays in the feedback can cause oscillations.

9

What are non-linear sensitivities? + example

Butterfly Effect: serious failures can occur if there are unplanned or uncontrolled interactions between the parts (non-linear sensitivities).

An example is Computer Based Trading (CBT) !!

10

What are overriding priorities in systems?

• transport system which must be safe
• satellite system which must be reliable

11

source of constraints

emergent properties

12

Six Principles for Integrated System Design

1. Debate, define, and revise the purpose
- build the business case

2. Think holistic
- look at all parts + environment + tools and methods
- manage entire timeline

3. Follow a systematic procedure (aka. the project management guidelines)

4. Be creative
- from simple to complex
- success metrics measure how closely the candidate design meets the goal
- trade-offs between requirements and system architecture may occur

5. Take people into account
- motivation, competence, quality, ergonomics, ethics and trust

6. Manage the project and the relationships
- design the project, not just the system
- project management
- be agile; collaboration

13

define a hazard and accident

a hazard can be controlled (food poisoning)

an accident/loss may be outside of our control (food products containing pathogens are sold)

14

Use the constraints to ...

- Design the system (constraints are system requirements)
- Determine what information is needed by the controller
- Write the system tests

15

draw a simple (closed-loop) feedback loop diagram

input-->controller-->process-->output-->sensor sends back output information to input

(e.g., human seeing car speed, central heating system)

16

How does Systems Theory relate to organisations?

Organisational success relies on synergy, interrelations and interdependence between different SUBSYSTEMS that are always changing.

17

What are open-loop control systems

No feedback mechanism and no control.

input --> transformation --> output

18

What are closed-loop control systems with humans?

Where the brain is the controller:

input [driving fast] --> process [measuring speed] --> output [speed display] --> controller [brain: go slower] --> links back to input [drives slower]

19

Some causes of failure in CBT systems

- Even small changes can have big effects (non-linear sensitivities)

- Incomplete, inaccurate, or outdated information held by some parties; less informed decisions

- High frequency trades fuel positive feedback loops within the system

20

How to do STAMP?

1. Identify the Accident or Loss
2. Identify the Hazards
3. Identify the Safety Constraints
4. Draw the Safety Control Structure

21

How to ensure a safe door mechanism in an elevator/train using STAMP?

1. Identify the previous accidents (or losses)
• what are the lessons-learned

2. Identify the Hazards
• train may move with doors open
• people stuck in doors
• no emergency door opener

3. Identify the Safety Constraints
• place warning signs
• add audio-visual signals for doors opening and closing
• install sensors in doors, rapidly stopping when object sensed
• install cushions on doors
• train accelerometer; train must only move when all doors are closed
• make train aware of its position; open doors only at station
• add emergency indicator
• install emergency door opener

4. Draw the Safety Control Structure
• n/a

22

What are Safety Constraints?

Safety constraints are another way of specifying safety-related requirements:

• A requirement is any mandatory, externally observable, verifiable (testable) behaviour, characteristic, or interface.

• A constraint is any engineering decision (e.g., design decision, implementation technique) that has been selected to be imposed as a requirement.

• A safety constraint specifies a specific safeguard (e.g., safety design feature, safety implementation technique).

Safety constraints typically include things like physical barriers around moving parts and electricity, handling toxic chemicals, and placing warning signs. However, designing an entirely new system, eliminated the need for safeguards, may be both cheaper and safer.