1. © J. Christopher Beck 20051 Lecture 31: Scheduling Systems 2

2. © J. Christopher Beck 2005 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

3. © J. Christopher Beck 2005 3 Scheduling Systems are Information Systems Everything you learned in your Information Systems Design Course 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, …

4. © J. Christopher Beck 2005 4 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?

5. © J. Christopher Beck 2005 5 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

6. © J. Christopher Beck 2005 6 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

7. © J. Christopher Beck 2005 7 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?

8. © J. Christopher Beck 2005 8 What Tool Does the Most to Increase Schedule Quality? Suppliers Customers Factory floor The rest of the information system

9. © J. Christopher Beck 2005 9 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?

10. © J. Christopher Beck 2005 10 What Does a Human Scheduler Do? 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

11. © J. Christopher Beck 2005 11 What Does a Human Scheduler Do? Spends money to relax constraints Can we run a 3 rd shift? Can we rent capacity from a competitor? Can we go below safety stock to meet this order?

12. © J. Christopher Beck 2005 12 What Does a Human Scheduler Do? 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?

13. © J. Christopher Beck 2005 13 The Scheduling Problem Scheduling Problem Customer Demand Forecast Demand Quality RequirementsResource Availabilities Process Plans Raw Material Supply Preventative Maintenance Union RegulationsMake or Buy? Order Priorities

14. © J. Christopher Beck 2005 14 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

15. © J. Christopher Beck 2005 15 Another View of Scheduling We should be building information systems that give humans the information required to make better decisions

16. © J. Christopher Beck 2005 16 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?

17. © J. Christopher Beck 2005 17 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

18. © J. Christopher Beck 2005 18 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

19. © J. Christopher Beck 2005 19 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 the assumptions made in the scheduling model

20. © J. Christopher Beck 2005 20 This is All Very Depressing (and an exaggeration) We’ve just spent 13 weeks learning about techniques that solve the wrong problem with the wrong data