Week 3 - Supply Chain Modelling

Question 1

What is a model

Answer 1

Is intended to represent a real system, either existing or planned

Question 2

What are the major advantages of a model? (2)

Answer 2

• It succinctly represents the real system
• When investigated you are able to discover things about the real system

Question 3

What is a system and it’s function? (2)

Answer 3

• Is a collection of interrelated components that work together towards a collective goal
• the function is to receive inputs and transform these into outputs

Question 4

Name 3 characteristics of systems

Answer 4

• Environment
• Organisation
• Interdependency

Question 5

Explain environment as a characteristic of systems

Answer 5

Systems are contained within an environment that contains other systems and external agencies and the scope of a system is defined by its boundary

Question 6

Explain organisation as a characteristic of systems

Answer 6

The components of a system work towards a collective goal known as the system’s objective

Question 7

Explain interdependency as a characteristic of a system

Answer 7

Systems are made up of subsystems (components) that may themselves being made up of other subsystems thus parts of a system are dependent on one another in some way

Question 8

What is combinatorial complexity?

Answer 8

Is when we have activities that have a 2 way relationship with every other activity

Question 9

How can the number of interconnections in combinatorial complexity be calculated?

Answer 9

n(n-1) where n is the number of activities

Question 10

What is dynamic complexity?

Answer 10

Can arise in systems due to feedback and delays for example between cause and effect

Question 11

What are the 2 main modelling methods?

Answer 11

• Descriptive modelling
• Explanatory modelling

Question 12

What is descriptive modelling? (2)

Answer 12

• Based on measuring observed behaviour
• If a system shows a certain regularity in behaviour then future behaviour may be predicted under the same conditions

Question 13

Name some examples of descriptive modelling (3)

Answer 13

• Regression analysis
• Data mining
• Machine learning

Question 14

What is explanatory modelling? (2)

Answer 14

• is based on a systems view and represents the real system structure
• It emphasises on the identification on the processes that are decisive for system behaviour

Question 15

What is a deterministic model?

Answer 15

Is a model that does not represent uncertainty and so for a given set of conditions and parameters will always produce the same outcome

Question 16

What does a deterministic model imply?

Answer 16

It implies that given a well enough detailed snapshot of a system we should be able to forecast the system’s dynamic behaviour perfectly thus are able to be analytically traceable and expressed as a mathematical formulae

Question 17

What does a stochastic model include? (2)

Answer 17

Includes some random component such as:
• variable demand rate
• variation or processing rates due to natural variability

Question 18

Benefit and drawback of stochastic models

Answer 18

• Models have an increased realism (benefit)
• (Drawback) make even simple models intractable

Question 19

3 Examples of static models

Answer 19

• Linear programming
• Spreadsheets
• Monte Carlo simulation

Question 20

How should models be developed? (According to Pidd 2009 applying the principles of Occam’s razor 1300)

Answer 20

Developed so that they are as simple as possible and yet are valid and useful for their intended purpose

Question 21

What are the general principles for model development? (4) (Robinson van der zee 2018)

Answer 21

• Focus on the decision, not the system
• Abstract - do not model all you know about the world
• The model should drive the data requirements and not the available data drive the model
• start small and add

Question 22

What is required when starting a simple model? (Brooks and Tobias 2000)

Answer 22

Requires us to define a number of simplifications to define what simple model

Question 23

What is a puzzle? (Pidd 2009)

Answer 23

Is a set of circumstances in which there is no ambiguity whatsoever once so,e thought has been given to what is happening or needs to be done

Question 24

What are the issues that need to be faced with puzzles? (3)

Answer 24

• entirely clear
• the range of options being completely known
• a single correct solution

Question 25

What is a problem?

Answer 25

Has no single answer but has several equally valid solutions

Question 26

What are messes? (2)

Answer 26

• Is a set of circumstances which there is extreme ambiguity and in which there may well be disagreement • There is a system of problems with multiple stakeholders with differing views

Question 27

What are the six principles of modelling? (Michael Pidd in ‘tools for thinking’)

Answer 27

• Model simple, think complicated • Be parsimonious, start simple and add • Divide and conquer, avoid mega-models • Use metaphors, analogies and similarities • Do not fall in love with the data • Model-building may feel like muddling through

Question 28

What does ‘divide and conquer, avoid mega-models’ mean?

Answer 28

Means breaking large general-purpose models down into simple models in order to better validate, interpret and explain

Question 29

What does ‘use metaphores, analogies and similarities’ mean? (4)

Answer 29

Means getting a variety of perspectives of a problem such as: • Personal • Direct - think of parallel situations from real life • fantasy - as the question ‘just suppose…’

Question 30

What does ‘do not fall in love with data’ mean?

Answer 30

Means data collection should be based around the modelling and only being collected in 3 types which are contextual, realisation and validation

Question 31

What is meant by a soft approach to modelling?

Answer 31

Concerned with problem structuring when it’s necessary to understand context and consider people’s opinions

Question 32

What is the impact of problem structuring in terms of a soft approach to modelling? (2)

Answer 32

• Can enable people to make better decisions • Could prelude to more formal mathematical modelling approaches

Question 33

Characteristics of soft approaches (4)

Answer 33

• Assume problem is not straight forward • Don’t assume organisations are just perfect intern of human labour functions and objectives • Has the idea that models are developed to help people to think through their own positions and engage in debate with other about possible actions • Stress the importance of organisational and individual learning

Question 34

Name 2 soft approaches to modelling

Answer 34

• Soft systems methodology • System dynamics

Question 35

What is soft systems methodology?

Answer 35

Is a way of using system ideas with human organisations to help humans make changes and understand their effects

Question 36

What is soft systems methodology method?

Answer 36

Move from an unstructured problem situation to a problem situation that is expressed with the purpose to uncover different perceptions of why the intervention is needed and what it is that appears to go on

Question 37

What is needed to be understand in soft systems methodology (method) (3)

Answer 37

• Structure - static aspects such as physical layout, power hierarchies and formal informal communication systems • Process - how things are done and what people are trying to do • Climate - the culture of the organisation

Question 38

The six components of a root definition

Answer 38

• Customers • Actors - human who carry out activities in a system • Transformation process - conversion from input to output • Weltanschauung - the world wide view that makes the root definition • Ownership - the individuals responsible for the system • Environmental constraints - such as legal, physical or ethical

Question 39

What are root definitions used for? (2)

Answer 39

• To develop a conceptual model showing the interconnections of the activities that must be present for the root definition to make sense • The conceptual model is then compare to the current situation to see what changes need to be made

Question 40

What is system dynamics?

Answer 40

Provides a way of viewing human systems by stressing the importance of certain structural features such as feedback control

Question 41

What are casual loop diagrams used for?

Answer 41

To understand the broad structure of a system and the elements are linked by arrows which indicate the direction of causality of the link

Question 42

What does a casual loop diagram/system archetype represent and the benefit of this?

Answer 42

A template of common behaviours in systems which provides a way of understanding the underlying dynamics to explain behaviour

Question 43

What do system dynamics models involve?

Answer 43

The construction of a dynamic simulation model where the stocks of variables are connected together via flows

Question 44

What computer software can implement SD simulation model? (3)

Answer 44

• Stella ll • Vensim • iThink

Question 45

Name 3 hard modelling approaches

Answer 45

• Linear programming • Simulation modelling • Heuristic search

Question 46

What are the set of assumptions for linear programming?

Answer 46

• a set of alternative courses of action • Knowledge and information that permit the prediction of the consequences of choosing any alternative • a criteria for determining which set of consequences is preferred

Question 47

Name the two types of simulations in simulation modelling?

Answer 47

• Static simulations • Dynamic simulations

Question 48

What are static simulations?

Answer 48

Are simulations that are not concerned with dynamics interactions through time and include monte Carlo simulation

Question 49

What are dynamic simulations?

Answer 49

Are simulations that are concerned with systems whose behaviour varies through time and include system dynamics, discrete event simulation and agent-based simulation

Question 50

Characteristics of systems best suited to the use of dynamic simulation (3)

Answer 50

• Dynamic • Interactive - system consists of a number of components that interacts and produces distinct behaviour of the system • Complicated

Question 51

What is a heuristic search? (2)

Answer 51

• Is similar in nature to simulations in terms of there being no guarantee that any proposed solution will be optimum • Provide ways of automatically generating solutions to problems that have been formulated in certain ways

Question 52

What do heuristic search approaches include? (3)

Answer 52

• Tabu search • Simulated annealing • Genetic algorithms

Question 53

What is a tabu search?

Answer 53

Rets on the procedures that declare certain search moves to be forbidden and in a heuristic search it will normally choose the lowest p-cost no-tabu neighbour

Question 54

What is simulated annealing?

Answer 54

Is simulated annealing the algorithms try to avoid convergence on local optima by careful control

Question 55

What are genetic algorithms?

Answer 55

Are from population genetics with the notion that circumstances temper random mutation by selecting some mutations as better suited to survival than others

Question 56

Where can soft systems methodology be applied? (4)

Answer 56

• cost drivers of maintenance operations • Supply chain design • Coordination in the supply chain • Contracting in the supply chain

Question 57

Where can system dynamics be applied? (5)

Answer 57

• Supply chain design • Resilience to disruptive events • Sustainability in the supply chain • Impact of mitigation policies in a pandemic • Impact of risks in the transportation system

Question 58

Where can linear programming be applied? (3)

Answer 58

• Supply network design • Scheduling • Vehicle routing

Question 59

Where can simulation modelling be applied? (5)

Answer 59

• Supply chain performance (SCOR) • Capacity planning • ‘last mile’ logistics • Food retail distribution • End-of-life reverse supply chain for electric vehicle batteries

Question 60

Where can a heuristic search be applied? (5)

Answer 60

• Facility location • Production time crashing • Inventory routing • Logistics route optimisation • Lot sizing