Learning Objectives
• Explain the key issues associated with project
management.
• Describe how to apply the Critical Path Method
(CPM).
• Explain how to make time/cost tradeoff
decisions in projects.
1–2
Understand the following terms:
1–3
- Network * Activities critical path
- Event *critical
activities - Critical Path
4
Network Diagrams
• Network diagrams are the preferred
technique for showing activity sequencing.
• A network diagram is a schematic display
of the logical relationships among, or
sequencing of, project activities.
• Two main formats are the arrow and
precedence diagramming methods.
Network Diagrams
Activity-on-Arrow (AOA) networks
– also called Arrow Diagramming Method (ADM)
– Uses an arrow to depict an activity
– simpler for projects with many dependencies
– emphasizes events; milestones can be easily flagged
– sometimes requires dummy activities
Activity-on-Node (AON) networks
– also called Precedence Diagramming Method (PDM)
– Uses a node to depict an activity
– easier to draw for simple projects
– emphasizes activities
– no dummy activities
6–6
Constructing a Project Network
• Terminology
– Event: a point in time when an activity is started
or completed. It does not consume time.
– Activity: an element of the project that requires
time.
– Merge Activity: an activity that has two or more
preceding activities on which it depends.
– Parallel (Concurrent) Activities: Activities that can
occur independently and, if desired,
not at the same time.
6–7
Constructing a Project Network
• Terminology
– Path: any route along the network from start to finish
– Critical path: the longest path through the activity
network that allows for the completion of all projectrelated
activities; the shortest expected time in which
the entire project can be completed. Delays on the
critical path will delay the completion of the entire
project.
(Assumes that minimum of A + B > minimum of C in
length of times to complete activities.)
3 4
5
2
6
A B
C
D
Situations in network diagram AON
2–8
Situations in network diagram AOA
A
B
C
A must finish before either B or C can start
A
B
C both A and B must finish before C can start
D
C
B
A
both A and B must finish before either of C or D can
start
A
C
B
D
Dummy
A must finish before B can start
both A and C must finish before D can start
2–9
A Comparison of AON and AOA Network
Conventions
Activity on Activity Activity on
Node (AON) Meaning Arrow (AOA)
A comes before
B, which comes
before C
(a) A B C
A B C
A and B must both
be completed
before C can start
(b)
A
C
B C
A
B
B and C cannot
begin until A is
completed
(c)
B
A
C
A
B
C
A Comparison of AON and AOA Network
Conventions
Activity on Activity Activity on
Node (AON) Meaning Arrow (AOA)
C and D cannot
begin until A
and B have
both been
completed
(d)
A
B
C
D B
A C
D
C cannot begin
until both A and B
are completed; D
cannot begin until
B is completed. A
dummy activity is
introduced in AOA
(e)
A C
B D
Dummy activity
A
B
C
D
A Comparison of AON and AOA Network
Conventions
Activity on Activity Activity on
Node (AON) Meaning Arrow (AOA)
B and C cannot
begin until A is
completed. D
cannot begin
until both B and
C are completed.
A dummy
activity is again
introduced in
AOA.
(f)
A
C
B D A B
C
D
Dummy
activity
darla/smbs/vit 13
AOA Project Network for House
A
2 0
C
3
E F
1 1 2 4 6 7
3
5
Lay
foundation
Design house
and obtain
financing
Order and
receive
materials
Dummy
Finish
work
Select
carpet
Select
paint
Build
house
AON Project Network for House
A3 B2
D3
C1
E1
F
1
G1
Start
Design house
and obtain
financing
Order and receive
materials Select paint
Select carpet
Lay foundations Build house
Finish work
2–13
3
B
1
D
1
1
G
Constructing a Project Network:
Table 3-1 A Sample Set of Project Activities and
Precedence’s Activities
2–14
Activity Predecessor
a —
b —
c a
d b
e b
f c, d
g e
Constructing a Project Network:
Figure 3-1 Stage 1 of a Sample AON Network
2–15
Constructing a Project Network:
Figure 3-2 Stage 2 of a Sample AON Network
2–16
Constructing a Project Network: Figure 3-3 A
Completed Sample AON Network
2–17
Critical Path Method (CPM)
Critical Path – path with the longest total duration
This is the shortest time in which the project can
be completed.
Critical Activity – an activity on the critical path
*If a critical activity is delayed, the entire
project will be
delayed. Close attention must be given to
critical activities
to prevent project delay. There may be
more than one
critical path.
Critical Path Method (CPM)
Practical approach to finding critical path:
- identify all possible paths from start to finish
- sum up durations for each path
- largest total indicates critical path
(This approach is inefficient, but is instructive)
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