CHAPTER 6 Scheduling

LEARNING OBJECTIVES A schedule is a timetable for a plan and cannot be established until the plan has been developed. In this chapter the student will become familiar with  estimating the duration for each activity  establishing the estimated start time and required completion time for the overall project  calculating the earliest times at which each activity can start and finish, based on the project’s estimated start time  calculating the latest times by which each activity must start and finish in order to complete the project by its required completion time  determining the amount of positive or negative slack between the time each activity can start or finish and the time it must start or finish  identifying the critical (longest) path of activities

TEACHING STRATEGIES 1. Ask the students what it means to do scheduling and why it is important. 2. Ask them if this can be done before the activities have been defined. Why or why not? 3. Ask them how they built their schedule of classes for the semester. What problems did they encounter? 4. Ask them how they determine how long a task will take. Give some examples of tasks and ask them to estimate the durations. 5. Give some real world examples from your experience.

LECTURE OUTLINE 1. Real-World Examples

A. Vignette: US Census 2000 Project

• A US Census takes place every 10 years in the form of a questionnaire from the US Census Bureau. • A population count is required by the US Constitution, and is used to allocate congressional representation and district boundaries. • Census information helps the government in making policies regarding health, education, transportation, community services, etc. • Census participation takes only a few minutes, but it takes years for the employees of the Census Bureau.

CHAPTER 6/Scheduliing 111 • Census 2000 was a 13-year project that’s total life cycle costs $65 billion. • Planning for data collection is important i. 520 local census offices across the US verify and collect as many addresses as possible in the Master Address File ii. Special procedures are used for data collection in different areas: a. Update/Leave procedure—rural areas with “rural route” address or post office boxes b. Mailout/Mailback process—standardized street addresses c. List/Enumerate procedure—census employees visit remote areas where the population changes with the seasons to personally collect the data. Most labor intensive of the three procedures • Project’s goal was 70% response rate to the 2000 Census. • The Bureau implemented a plan to spread the word about the census and stressed its importance. i. Partnerships were formed with Congress, local leaders, and educators to inform as many people as possible ii. Paid advertising began a year before the census on billboards, television, radio, and magazines iii. A non-response follow-up plan was created- estimated that Census employees would visit 46 million households to speak to those that did not complete the census iii. Lockheed Martin and TRW worked with the Bureau to test the data collection system using optical character recognition (OCR) software • The 2000 Census was considered to be the most accurate population count in US history. For the first time, census data was made available on the Internet.

B. Vignette: High Risk Projects at NASA

• The Genesis spacecraft returned to earth on September 2, 2004, but the landing didn’t go as planned. • The parachute was supposed to deploy, so it could be intercepted by a helicopter crew. • Instead, the $264 million spacecraft fell toward the earth at an estimated 193 miles per hour. • The spacecraft had collected particles that represent the earliest forms of matter in the solar system. With the unexpected landing, this research was in jeopardy. • The team was able to implement the contingency plan they developed in case the parachute didn’t work:

112 CHAPTER 6/Scheduling i. This included safety precautions so explosive devices wouldn’t explode upon handling. ii. Sample extraction was used to salvage the samples collected. • Luckily, the spacecraft landed on moist desert floor, and most of the craft remained in tact. • NASA will apply lessons learned in this project to their next project: Stardust. i. Stardust is scheduled to land in 2006. ii. It is supposed to land by parachute (like Genesis) carrying cargo from the comet Wild 2. • A contingency plan has been made in advance to stay on track for this project while managing risks.

2. Activity Duration Estimates A. The first step in establishing a project schedule is to estimate how long each activity will take. B. This duration estimate for each activity is the total elapsed time for the work to be done plus any associated waiting time. C. Display and discuss Figures 6.1 and 6.2. D. The person responsible for performing a particular activity should help make the duration estimate. However, for large projects it may not be practical to have each person provide activity duration estimates. E. An activity’s duration estimate must be based on the quantity of resources expected to be used on the activity. F. Figures 6.3 and 6.4 show network diagrams for a consumer market study in the AIB and AOA formats, respectively.

3. Project Start and Finish Times A. It’s necessary to select an estimated start time and a required completion time for the overall project. B. The project’s required completion time is normally part of the project objective and is stated in the contract. C. If a project must be completed in 130 working days, we define the project’s estimated start time as 0 and its required completion time as day 130.

4. Schedule Calculations A project schedule provides a timetable for each activity and shows 1. the earliest times (or dates) at which each activity can start and finish, based on the project's estimated start time (or date) 2. the latest times (or dates) by which each activity must start and finish in order to complete the project by its required completion time (or date)

A. Earliest Start and Finish Times

CHAPTER 6/Scheduliing 113 1. Earliest start time (ES) is the earliest time at which a particular activity can begin. 2. Earliest finish time (EF) is the earliest time by which a particular activity can be completed. EF = ES + Duration Estimate 3. The ES and EF times are determined by calculating forward through the network diagram. 4. Rule 1: The earliest start time for a particular activity must be the same as or later than the latest of all the earliest finish times of all the activities leading directly into that particular activity. 5. Display and discuss Figure 6.5. 6. Display and work through the calculations in Figures 6.6 and 6.7 with the class. 7. The ES and EF times are sometimes listed in a separate schedule table, like the one in Figure 6.8.

B. Latest Start and Finish Times 1. Latest finish time (LF) is the latest time by which a particular activity must be finished in order for the entire project to be completed by its required completion time, calculated on the basis of the project’s required completion time and the duration estimates for succeeding activities. 2. Latest start time (LS) is the latest time by which a particular activity must be started in order for the entire project to be completed by its required completion time, calculated by subtracting the activity’s duration estimate from the activity’s latest finish time: LS = LF – Duration Estimate 3. The LF and LS times are determined by calculating backward through the network diagram. 4. Rule 2: The latest finish time for a particular activity must be the same as or earlier than the earliest of all the latest start times of all the activities emerging directly from that particular activity. 5. Display and discuss Figure 6.9. 6. Display and work through the calculations in Figures 6.10 and 6.11 with the class. 7. The very first activity, “Identify Target Consumers,” has an LS of –8! This means that in order to complete the entire project by its required completion time of 130 days, the project must start 8 days earlier than it is estimated to start. 8. Like the earliest start and earliest finish times, the latest start and latest finish times are sometimes shown in a separate schedule table (see Figure 6.12).

C. Total Slack 1. The difference between the calculated earliest finish time of the very last activity and the project’s required completion time is the total slack (TS), sometimes called float.

114 CHAPTER 6/Scheduling 2. If total slack is positive, it represents the maximum amount of time that the activities on a particular path can be delayed without jeopardizing completion of the project by its required completion time. 3. On the other hand, if total slack is negative, it represents the amount of time that the activities on a particular path must be accelerated in order to complete the project by its required completion time.

Total Slack = LF – EF or Total Slack = LS – ES

D. Critical Path 1. This longest path in the overall network diagram is called the critical path. 2. One way to determine which activities make up the critical path is to find which ones have the least slack. 3. All the activities with this value are on the critical path of activities. 4. The values of total slack for the consumer market study project are shown in Figure 6.13. 5. The lowest value is –8 days. 6. The activities that have this same value of total slack make up the path 1–2–3– 4–6–9–11–12–13. 7. To eliminate the –8 days of slack, the estimated durations of one or more activities on this critical path need to be reduced. 8. Suppose we reduce the estimated duration of “Mail Questionnaire & Get Responses” from 65 days to 55 days. The total slack changes from –8 days to +2 days. 9. Those paths with positive values of total slack are sometimes referred to as noncritical paths, while those paths with zero or negative values of total slack are referred to as critical paths. 10. In this case the longest path is often referred to as the most critical path.

E. Free Slack 1. Free slack is the amount of time a particular activity can be delayed without delaying the earliest start time of its immediately succeeding activities. 2. It is the relative difference between the amounts of total slack for activities entering into the same activity. 3. It is always a positive value. 4. In the network diagram (Figure 6.14), there are three instances where a particular activity has more than one activity entering into it:  Activity 9, “Mail Questionnaire & Get Responses,” has activities 5 and 6 entering into it.  Activity 10, “Test Software,” has activities 7 and 8 entering into it.  Activity 11, “Input Response Data,” has activities 9 and 10 entering into it. 5. The values of total slack for activities 5 and 6 are 0 and –8 days, respectively. 6. The lesser of these two values is –8 days for activity 6.

CHAPTER 6/Scheduliing 115 7. The free slack for activity 5 is the relative difference between its total slack, 0, and –8. This relative difference is 8 days: 0 – (–8) = 8 days.

5. Scheduling for Information Systems Development Among the common problems that often push IS development projects beyond their required completion time are the following:  Failure to identify all user requirements  Failure to properly identify user requirements  Continuing growth of project scope  Underestimating learning curves for new software packages  Incompatible hardware  Logical design flaws  Poor selection of software  Failure to select the best design strategy  Data incompatibility issues  Failure to perform all phases of the SDLC

Without looking ahead in the book, have the students draw the network and perform the calculations based on Figure 6.17.

6. Project Management Software A. Almost all project management software packages allow you to perform the scheduling functions identified in this chapter. B. Activity durations can be estimated in hours, days, weeks, months, or years. C. Project start and finish times can be entered as specific calendar dates (for example, June 1, 2002 and December 1, 2002), or an overall number of days (or weeks or months). D. The software will calculate the date by which a project needs to start. E. Similarly, it will calculate the earliest project completion date, based on the actual start date and the list of activities with their estimated durations. F. The software will also calculate ES, EF, LS, and LF times, total and free slack, and the critical path, all with a click of the mouse. G. See Appendix A for a thorough discussion of project management software.

QUESTIONS 1. Why does the scheduling function depend on the planning function? Which one must be done first? Why? A schedule is a timetable for a plan and cannot be established until the plan has been developed.

2. Describe what an activity duration estimate is. How is it determined? Can an activity have an estimated duration of 0? Why or why not?

116 CHAPTER 6/Scheduling The duration estimate for each activity is the total elapsed time for the work to be done plus any associated waiting time. An activity’s duration estimate must be based on the quantity of resources expected to be used on the activity. The estimate should be aggressive, yet realistic. A Beta distribution using most likely, pessimistic, and optimistic times can be used.

Yes, a dummy activity in the AOA format has a duration of 0 and does not consume any time.

3. Why might a contractor prefer to state a project completion time in terms of a number of days after the project starts rather than a specific date? Give some examples of instances when this would be appropriate. This is helpful in case the start of the project is delayed for some reason, such as an unexpected snowstorm delaying the start of a construction project.

4. Refer to Figures 6.6 and 6.7. Why is the earliest start time for “Review Comments & Finalize Questionnaire” day 33? Why is the earliest finish time day 38? The task can’t start until its predecessor is finished, which is day 33. It has a duration of 5, so it will finish at day 38.

5. Refer to Figures 6.10 and 6.11. Why is the latest start time for “Mail Questionnaires & Get Responses” day 40? Why is the latest finish time day 105? Since it predecessor’s latest start time is day 105, it must finish by day 105. It has a duration of 65, so it must start by day 40.

6. What is meant by the term slack as applied to a particular activity? What is the difference between positive slack and negative slack? How is it calculated? Slack is the amount of time an activity’s earliest finish time can be delayed without delaying succeeding tasks beyond their latest finish times. If it is positive you have extra time that can be used if needed. If it is negative, the activity needs to be completed by its latest finish time or the project completion will be delayed. Slack = LF – EF or Slack = LS – ES

7. What is meant by the term total slack as applied to a path? When is a path considered to be a critical path? Total slack, if it’s a positive value, is the amount of time that the activities on a particular path can be delayed without jeopardizing completion of the project by its required completion time. If it’s a negative value, it is the amount of time that the activities on a particular path must be accelerated in order to complete the project by its required completion time. Those paths with positive values of total slack are sometimes referred to as noncritical paths, while those paths with zero or negative values of total slack are

CHAPTER 6/Scheduliing 117 referred to as critical paths. In this case the longest path is often referred to as the most critical path.

8. Why is it important to determine the critical path of a project? What happens if activities on this path are delayed? What happens if activities on this path are accelerated? If any activity on the critical path is delayed, the whole project will be delayed, so it is important to know what the critical path is. If any of these activities are accelerated, the project completion date will also be accelerated.

9. Why is the scheduling of IS projects so challenging? What are some of the common problems that push IS projects beyond their due dates? Scheduling for IS is often done in a haphazard manner, and thus a large percentage of IS projects are finished much later than originally promised or never finished at all. One of the most important factors in effective scheduling is arriving at activity duration estimates that are as realistic as possible. Among the common problems that often push IS development projects beyond their required completion time are the following:  Failure to identify all user requirements  Failure to properly identify user requirements  Continuing growth of project scope  Underestimating learning curves for new software packages  Incompatible hardware  Logical design flaws  Poor selection of software  Failure to select the best design strategy  Data incompatibility issues  Failure to perform all phases of the SDLC

118 CHAPTER 6/Scheduling 10. Calculate the ES, EF, LS, and LF times and the slack for each activity in the figure below and identify the critical path for the project. Can the project be completed in 40 weeks? Activity ED ES EF LS LF TS A 2 0 2 4 6 4

B 10 2 12 6 16 4 C 8 2 10 7 15 5 D 15 2 17 8 23 6 E 7 12 19 16 23 4 F 20 10 30 15 35 5 G 12 19 31 23 35 4 H 5 31 36 35 40 4 Yes, the project can be completed within 40 weeks. With the current estimates, it will take 36 weeks. The longest path in the network is: A – B – E – G – H.

11. Calculate the ES, EF, LS, and LF times and the slack for each activity in the figure below and identify the critical path for the project. Can the project be completed in 30 weeks? Activity ED ES EF LS LF TS 1. Prob. Def. 2 0 2 -5 -3 -5

2. Sys. Analysis 5 2 7 -3 2 -5 3. Design I/O 3 7 10 6 9 -1 4. Design DB 15 7 22 2 17 -5 5. Develop Input 8 10 18 11 19 1 6. Develop Output 10 10 20 9 19 -1 7. Develop DB 2 22 24 17 19 -5 8. Test System 6 24 30 19 25 -5 9. Implement 5 30 35 25 30 -5

No, this project cannot be completed within 30 weeks. With the current estimates, it will take 35 weeks. The most critical path is: 1-2-4-7-8-9.

12. Calculate the ES, EF, LS, and LF times and the slack for each activity in the figure below and identify the critical path for the project. Can the project be completed in 30 weeks?

Activity ED ES EF LS LF TS A 3 0 3 2 5 2

B 5 0 5 -2 3 -2

CHAPTER 6/Scheduliing 119 C 18 3 21 5 23 2 D 7 5 12 3 10 -2 E 10 5 15 5 15 0 F 5 12 17 10 15 -2 G 8 17 25 15 23 -2 H 2 25 27 23 25 -2 I 9 17 26 16 25 -1 J 5 27 32 25 30 -2

No, this project cannot be completed within 30 weeks. With the current estimates, it will take 32 weeks. The most critical path in the network is: B – D – F – G – H – J

WORLD WIDE WEB EXERCISES Assign the World Wide Web Exercises to your students as homework or complete them together in a computer lab.

CASE STUDY #1 A NOT-FOR-PREOFT MEDICAL RESEARCH CENTER This is an open-ended case study. The students have the opportunity to be very creative on this one. Encourage that creativity.

Answers to Case Questions * Answers will vary from student to student for each question.

1. Develop a duration estimate for each activity. 2. Using a project start time of 0 (May 15) and a required project completion time of 180 days (November 15), calculate the ES, EF, LS and LF times and Total Slack for each activity. (Note, if your calculations result in a project schedule with negative total slack, don’t make any revisions to any activity duration estimates or other changes to the network at this time. This will be done in the next chapter [7]). 3. Determine the critical path and identify the activities that make up the critical path. 4. Develop a cost estimate for each activity and determine the total budget for the project.

Group Activity Form groups of three or four members. Have each group perform the above tasks. Allow each group to present their answers.

120 CHAPTER 6/Scheduling CASE STUDY #2 THE WEDDING This is an open-ended case study. The students have the opportunity to be very creative on this one. Encourage that creativity.

Answers to Case Questions * Answers will vary from student to student for each question.

1. Develop a duration estimate for each activity. 2. Using a project start time of 0 (January 1) and a required project completion time of 180 days (June 30), calculate the ES, EF, LS and LF times and Total Slack for each activity. (Note, if your calculations result in a project schedule with negative total slack, don’t make any revisions to any activity duration estimates or other changes to the network at this time. This will be done in the next chapter [7]). 3. Determine the critical path and identify the activities that make up the critical path. 4. Develop a cost estimate for each activity and determine the total budget for the project.

Group Activity Form groups of three or four members. Have each group perform the above tasks. Allow each group to present their answers.

HOMEWORK 1. Have them read the real-world vignettes. 2. Have them read the chapter and answer all of the Reinforce Your Learning questions and the questions at the end of the chapter.

APPENDIX #1 - PROBABILITY CONSIDERATIONS

LECTURE OUTLINE A. Activity Duration Estimates 1. With projects for which there is a high degree of uncertainty about the activity duration estimates, it is possible to use three estimates for each activity:  Optimistic time (to) is the time in which a particular activity can be completed if everything goes perfectly well.  Most likely time (tm) is the time in which a particular activity can most frequently be completed under normal conditions.  Pessimistic time (tp) is the time in which a particular activity can be completed under adverse circumstances. 2. Establishing three time estimates makes it possible to take uncertainty into account when estimating how long an activity will take.

CHAPTER 6/Scheduliing 121 B. The Beta Probability Distribution 1. In network planning, when three time estimates are used for each activity, it is assumed that the three estimates follow a beta probability distribution. 2. The expected duration is calculated using the following formula:

te = F((to + 4(tm) + tp)/6) 3. Assume that the optimistic time for an activity is 1 week, the most likely time is 5 weeks, and the pessimistic time is 15 weeks. The expected duration for this activity is

te = F((1 + 4(5) + 15)/6) = 6 weeks C. Probability Fundamentals 1. Network planning in which three time estimates are used for each activity can be considered a stochastic, or probabilistic, technique, since it allows for uncertainty. 2. Any technique that uses only one time estimate is considered to be a deterministic technique. If only one time estimate is used for each activity, probability calculations cannot be made. 3. The central limit theorem of probability theory states that this total probability distribution is not a beta probability distribution but a normal probability distribution. 4. The variance for the beta probability distribution of an activity is found with the following formula:

Variance = 2 = BBC((F(tp – to,6))2 5. Note that the variance of the normal distribution is the sum of the variances of the beta distribution. 6. The standard deviation, , is another measure of the dispersion of a distribution and is equal to the square root of the variance. 7. The total probability distribution of all the activities on the critical path of a network diagram is a normal distribution, with a mean equal to the sum of the individual activity expected durations and a variance equal to the sum of the individual activity variances. 8. Review the example presented in the book.

D. Calculating Probability 1. In order to find the probability of actually completing a project before its required completion time, the following formula is used:

Z = F(LF – EF,t) 2. The elements in this formula are as follows:  LF is the required completion time (latest finish) for the project.

122 CHAPTER 6/Scheduling  EF is the earliest expected finish time for the project (mean of the normal distribution).  t is the standard deviation of the total distribution of the activities on the longest (or slowest) path leading to project completion. 3. In the above equation, Z measures the number of standard deviations between EF and LF on the normal probability curve. 4. Review the example presented in the book.

QUESTIONS 1. True or false: In order to calculate the probability of finishing a project by its required completion time, it is necessary to have three time estimates for each activity and the required completion time for the project. True.

2. What are the expected duration, variance, and standard deviation for an activity whose three time estimates are to = 2, tm = 14, and tp = 14? Expected duration = [2 + 4(14) + 14] / 6 = 72 / 6 = 12 Variance = [(14 - 2)/6]2 = 4.0 Standard deviation = 2.0

3. Which of the following is not a measure of the dispersion, or spread, of a distribution: variance, mean, or standard deviation? The mean is not a measure of dispersion.

4. The earliest expected finish time for a project is 138 days, and its required completion time is 130 days. What is the probability of completing the project before its required time if t (the standard deviation of the total distribution of the activities on the longest path) is 6? Z = 130 – 138 / 6 = –1.33 Using Table 6.1, the probability of completing the project between 130 and 138 days is 40.824%. To determine the probability of completing the project before 130 days, you need to subtract 0.40824 from 0.5000. Therefore, there is a 9.176% probability of completing the project by its required completion time of 130 days.

APPENDIX #2 - MICROSOFT PROJECT The Appendix in this chapter continues discussing Microsoft Project. Get the students to produce the diagrams that are shown in the chapter.

CHAPTER 6/Scheduliing 123