Project Management CH9 Project Scheduling

Chapter 9
Project Scheduling: Networks,
Duration Estimation, and
Critical Path
09-01

Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
Chapter 9 Learning Objectives
After completing this chapter, students will be able to:
 Understand and apply key scheduling terminology.
 Apply the logic used to create activity networks,
including predecessor and successor tasks.
 Develop an activity network using Activity-on-Node
(AON) techniques.
 Perform activity duration estimation based on the
use of probabilistic estimating techniques.
09-02

Chapter 9 Learning Objectives
After completing this chapter, students will be able to:
 Construct the critical path for a project schedule
network using forward and backward passes.
 Identify activity float and the manner in which it is
determined.
 Calculate the probability of a project finishing on time
under PERT estimates.
 Understand the steps that can be employed to reduce
the critical path.
09-03

Project Scheduling
 Project scheduling requires us to follow some
carefully laid-out steps, in order, for the schedule
to take shape.
 Project planning, as it relates to the scheduling
process, has been defined by the PMBoK as:
The identification of the project objectives and the
ordered activity necessary to complete the project
including the identification of resource types and
quantities required to carry out each activity or task.
09-04

Project Scheduling Terms
• Successors
• Predecessors
• Network diagram
• Serial activities
• Concurrent activities
09-05
ED
C
B
A F

Project Scheduling Terms
09-06
ED
C
B
A F
• Merge activities
• Burst activities
• Node
• Path
• Critical Path

FIGURE 9.2 Alternative Activity Networks for Term Paper Assignment
Network Diagrams
09-07

AOA Versus AON
The same mini-project is shown with activities
on arc…
09-08
C
ED
B F
E
C
D
B F
…and activities on node.

Node Labels
09-9
Early Start
Activity Float
Activity Descriptor
Late Start
ID Number
Activity Duration Late Finish
Early Finish

FIGURE 9.4
Activity Node Labels Using MS Project
2010
09-10

FIGURE 9.5
Serial Activities
09-11
Serial activities are those that flow from one to
the next, in sequence.

FIGURE 9.6
Activities Linked in Parallel
(Concurrent)
09-12
When the nature of the work allows for more than one activity
to be accomplished at the same time, these activities are called
concurrent and parallel project paths are constructed through the
network.

FIGURE 9.7
Merge Activity
09-13

FIGURE 9.8
Burst Activity
09-14

FIGURE 9.10
Complete Activity Network
09-15

FIGURE 9.11
Developing the Activity Network
Using MS Project 2010
09-16

Duration Estimation Methods
• Past experience
• Expert opinion
• Mathematical derivation – Beta
distribution
– Most likely (m)
– Most pessimistic (b)
– Most optimistic (a)
4
= TE
6
a m b
Activity Duration
09-17
2
2
=
6
b a
Activity Variance s

FIGURE 9.14 Symmetrical (Normal) Distribution for
Activity Duration Estimation
09-18

FIGURE 9.15 Asymmetrical (Beta) Distribution for Activity Duration Estimation
09-19

Activity Duration and Variance
09-20
Name: Project Delta
Durations are listed in weeks
Activity Description Optimistic Likely Pessimistic
A Contract signing 3 4 11
B Questionnaire design 2 5 8
C Target market ID 3 6 9
D Survey sample 8 12 20
E Develop presentation 3 5 12
F Analyze results 2 4 7
G Demographic analysis 6 9 14
H Presentation to client 1 2 4
Table 9.2

Constructing the Critical Path
• Forward pass – an additive move through the
network from start to finish
• Backward pass – a subtractive move through
the network from finish to start
• Critical path – the longest path from end to
end which determines the shortest project
length
09-21

Rules for Forward/Backward Pass
Forward Pass Rules (ES & EF)
– ES + Duration = EF
– EF of predecessor = ES of successor
– Largest preceding EF at a merge point becomes EF
for successor
Backward Pass Rules (LS & LF)
– LF – Duration = LS
– LS of successor = LF of predecessor
– Smallest succeeding LS at a burst point becomes
LF for predecessor 09-22

Project Delta Information
09-23
Project Delta
Activity Description Predecessors Estimated Duration
A Contract signing None 5
B Questionnaire design A 5
C Target market ID A 6
D Survey sample B, C 13
E Develop presentation B 6
F Analyze results D 4
G Demographic analysis C 9
Table 9.4

FIGURE 9.16 Partial Project Activity Network with Task Durations
09-24

FIGURE 9.18 Activity Network with Forward Pass
09-25

FIGURE 9.19 Activity Network with Backward Pass
09-26

FIGURE 9.20 Project Network with Activity Slack and Critical Path
Note: Critical path is indicated with bold arrows.
09-27

FIGURE 9.24
AON Network with Laddering
Effect
09-28

Laddering Activities
Project ABC can be completed more efficiently
if subtasks are used
09-29
A(3) B(6) C(9) ABC=18 days
Laddered
ABC=12 days
A1(1) A2(1) A3(1)
B1(2) B2(2) B3(2)
C1(3) C2(3) C3(3)

FIGURE 9.25
Example of a Hammock Activity
09-30

Reducing the Critical Path
• Eliminate tasks on the CP
• Convert serial paths to parallel when possible
• Overlap sequential tasks
• Shorten the duration on critical path tasks
• Shorten
– early tasks
– longest tasks
– easiest tasks
– tasks that cost the least to speed up 09-31

Summary
1. Understand and apply key scheduling terminology.
2. Apply the logic used to create activity networks,
including predecessor and successor tasks.
3. Develop an activity network using Activity-on-Node
(AON) techniques.
4. Perform activity duration estimation based on the
use of probabilistic estimating techniques.
09-32

Summary
5. Construct the critical path for a project schedule
network using forward and backward passes.
6. Identify activity float and the manner in which it is
determined.
7. Calculate the probability of a project finishing on
time under PERT estimates.
8. Understand the steps that can be employed to
reduce the critical path.
09-33

09-34

Project Management CH9 Project Scheduling

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