© j. christopher beck 20081 lecture 32: scheduling systems 2

© J. Christopher Beck 2008 1

Lecture 32: Scheduling Systems 2


Outline Scheduling Systems are

Information Systems But even harder to build

Are We Solving the Right Problem? What does a human scheduler do? Are we solving the “real” problem? Garbage in, garbage out


Readings

P Ch 13.7


Scheduling Systems are Information Systems

Everything you learned in MIE350 applies here 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, …


But It’s Worse

At the core is (usually) a mathematically hard problem

Risk & uncertainty If such a high percentage of normal IT

projects fail, what about projects where the core mathematical problem is intractable?


And Even Worse

Scheduling experts tend to be interested in the math and algorithms 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

one reason why InfoEng is important to OR people and why MIE350 is a core course


And Worse Again

“… 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


And Worse Again

“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


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?


What Tool Does the Most to Increase Schedule Quality?

Suppliers

Customers

Factoryfloor

The rest of theinformation

system


What Does a Human Scheduler Do?

Negotiates 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?



Prioritizes 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



Spends money to relax constraints Can we run a 3rd shift? Can we rent capacity

from a competitor? Can we go below safety

stock to meet this order?



Changes the problem! We have no mid-size

cars, would you like an SUV?

We have no tables available at 8 PM, how about 7:30?


The Scheduling Problem

SchedulingProblem

Customer Demand

Forecast Demand

Quality Requirements Resource Availabilities

Process Plans

Raw Material Supply

Preventative Maintenance

Union RegulationsMake or Buy?

Order Priorities


Changing the Problem

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! Think of the experience and information that the human needs


Another View of Scheduling

We should be building information systems that give humans the information required to make better decisions


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?


Real World Scheduling [MacKay88] “Pathological” job shop

80 acts/job, 300 res, 5000 active jobs all orders are behind schedule

Uncertainty 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


Uncertainty

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


In practice …

The shop floor deals with the problem 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 theassumptions madein the schedulingmodel


This is All Very Depressing

We’ve just spent 13 weeks learning about techniques that solve the wrong problem with the wrong data

© j. christopher beck 20081 lecture 32: scheduling systems 2

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