project scheduling: networks, duration estimation, and critical path
DESCRIPTION
Project Scheduling: Networks, Duration Estimation, and Critical Path. Chapter 9. B. A. D. E. F. C. Project Scheduling Terms. Successors Predecessors Network diagram Serial activities Concurrent activities. B. A. D. E. F. C. Project Scheduling Terms. Merge activities - PowerPoint PPT PresentationTRANSCRIPT
9-1
Project Scheduling: Networks, Duration Estimation,
and Critical Path
Chapter 9
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall
9-2
Project Scheduling Terms
• Successors
• Predecessors
• Network diagram
• Serial activities
• Concurrent activities
ED
C
B
A F
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9-3
Project Scheduling Terms
ED
C
B
A F
• Merge activities
• Burst activities
• Node
• Path
• Critical Path
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall
9-4
Network Diagrams
Show interdependence
Facilitate communication
Help schedule resources
Identify critical
activities
Determine project completion
Show start & finish dates
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9-5
AOA Vs. AON
The same mini-project is shown with activities on arc…
C
ED
B F
E
C
DB F
…and activities on node.
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9-6
Node Labels
Early Start
Activity Float Activity Descriptor
Late Start
ID Number
Activity Duration
Late Finish
Early Finish
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9-7
Duration Estimation Methods
• Past experience• Expert opinion• Mathematical derivation – Beta distribution
– Most likely (m)– Most pessimistic (b)– Most optimistic (a)
22 =
6
b aActivity Variance s
4 = TE
6
a m bActivity Duration
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9-8
Task Predecessor a b c
Z -- 7 8 15
Y Z 13 16 19
X Z 14 18 22
W Y, X 12 14 16
V W 1 4 13
T W 6 10 14
S T, V 11 14 19
1. Sketch the network described in the table.
2. Determine the expected duration and variance of each activity.
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9-9
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
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9-10
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
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9-11
Task Predecessor Time
A -- 4
B A 9
C A 11
D B 5
E B 3
F C 7
G D, F 3
H E, G 2
K H 1
1. Sketch the network described in the table.
2. Determine the ES, LS, EF, LF, and slack of each activity
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall
9-12
Laddering Activities
Project ABC can be completed more efficiently if subtasks are used
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)Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall
9-13
Hammock Activities
Used as summaries for subsets of activities
0 A 5
0 5 5
5 B15
5 1015
15 C 18
15 3 18
0 Hammock 18
0 18 18
Useful with a complex project or one that has
a shared budgetCopyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall
9-14
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
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall 9-15