Lecture 32:
Scheduling Systems 2
© J. Christopher Beck 2008
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Outline
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Scheduling Systems are Information
Systems
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But even harder to build
Are We Solving the Right Problem?
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What does a human scheduler do?
Are we solving the “real” problem?
Garbage in, garbage out
© J. Christopher Beck 2008
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Readings
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P Ch 13.7
© J. Christopher Beck 2008
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Scheduling Systems are
Information Systems
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Everything you learned in MIE350
applies here
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Why do you build a system?
How do you build a system?
How does the system get used in an
organization?
Use cases
Data modeling, process modeling, …
© J. Christopher Beck 2008
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But It’s Worse
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At the core is (usually) a mathematically
hard problem
Risk & uncertainty
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If such a high percentage of normal IT
projects fail, what about projects where
the core mathematical problem is
intractable?
© J. Christopher Beck 2008
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And Even Worse
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Scheduling experts tend to be
interested in the math and algorithms
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They may not talk to the “real users” or
may be even the system builders!
People who understand OR are not the
people who understand information
systems
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one reason why InfoEng is important to OR
people and why MIE350 is a core course
© J. Christopher Beck 2008
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And Worse Again
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“… a certain proportion of the
theoretical research done over the last
couple of decades is of very limited use
in real world applications”
– Pinedo p. 339
© J. Christopher Beck 2008
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And Worse Again
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“40 years of research in nurse
scheduling and “very few of the
developed approaches are suitable for
directly solving real world problems”
– Burke et al. p. 469
© J. Christopher Beck 2008
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Are We Solving the Right
Problem?
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Scheduling is important in the real
world
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economically, environmentally, …
To advance scheduling should we
concentrate on the OR or the
Information Engineering?
What is the right problem?
© J. Christopher Beck 2008
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What Tool Does the Most to
Increase Schedule Quality?
Suppliers
The rest of the
information
system
Factory
floor
Customers
© J. Christopher Beck 2008
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What Does a Human
Scheduler Do?
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Negotiates
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Can I deliver half now and
half later?
Can I substitute product X
for product Y?
Can you push this job
through the factory faster?
© J. Christopher Beck 2008
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What Does a Human
Scheduler Do?
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Prioritizes
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Job X is more important
because the customer is
very big
Job Y is more important
because we delivered their
order late last time
Job Z is more important because we are
phasing out that product
© J. Christopher Beck 2008
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What Does a Human
Scheduler Do?
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Spends money to relax
constraints
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Can we run a 3rd shift?
Can we rent capacity from
a competitor?
Can we go below safety
stock to meet this order?
© J. Christopher Beck 2008
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What Does a Human
Scheduler Do?
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Changes the problem!
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We have no mid-size cars,
would you like an SUV?
We have no tables
available at 8 PM, how
about 7:30?
© J. Christopher Beck 2008
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The Scheduling Problem
Customer Demand
Order Priorities
Raw Material Supply
Process Plans
Forecast Demand
Scheduling
Problem
Make or Buy?
Union Regulations
Quality Requirements
© J. Christopher Beck 2008
Resource Availabilities
Preventative Maintenance
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Changing the Problem
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Optimization techniques try to solve the
problem  human changes the
problem so it can be solvable!
What the human scheduler does is
based on knowledge not represented in
the scheduling problem!
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Think of the experience and information
that the human needs
© J. Christopher Beck 2008
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Another View of Scheduling
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We should be building information
systems that give humans the
information required to make better
decisions
© J. Christopher Beck 2008
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Are We Solving the Right
Problem?

Scheduling is important in the real
world



economically, environmentally, …
To advance scheduling should we
concentrate on the OR or the
Information Engineering?
What is the right problem?
© J. Christopher Beck 2008
18
Real World Scheduling
[MacKay88]
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“Pathological” job shop
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80 acts/job, 300 res, 5000 active jobs
all orders are behind schedule
Uncertainty
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set-up time varies from 2 days to 6 weeks
processing time: can vary by 100%
raw material arrival
high-priority orders
decreased worker productivity
© J. Christopher Beck 2008
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Uncertainty
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We don’t really know the exact
processing time of an activity
We don’t know when new orders will
arrive or if/when existing orders will be
cancelled
We don’t know when machines will
break down or how long it will take to
fix them
© J. Christopher Beck 2008
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In practice …
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The shop floor deals with the problem
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but what relation does the executed
schedule have to the original schedule?
A schedule is only “optimal” to the
extent that the real world follows the
assumptions made
in the scheduling
model
© J. Christopher Beck 2008
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This is All Very Depressing
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We’ve just spent 13 weeks learning
about techniques that solve the wrong
problem with the wrong data
© J. Christopher Beck 2008
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