project network

Project
• “A project is a series of activities directed to
accomplishment of a desired objective.”
Plan your work first…..then work your plan

Network analysis
Introduction
Network analysis is the general name given to certain specific
techniques which can be used for the planning, management and
control of projects.
One definition of a project:
“A project is a temporary endeavour undertaken to create a "unique" product
or service”

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• Graphical portrayal of activities and event
• Shows dependency relationships between
tasks/activities in a project
• Clearly shows tasks that must precede
(precedence) or follow (succeeding) other tasks
in a logical manner
• Clear representation of plan – a powerful tool for
planning and controlling project
NETWORK

CPM - Critical Path Method
• Definition: In CPM activities are shown as a network of precedence
relationships using activity-on-node network construction
– Single estimate of activity time
– Deterministic activity times
USED IN : Production management - for the jobs of repetitive in
nature where the activity time estimates can be predicted with
considerable certainty due to the existence of past experience.

PERT -
Project Evaluation & Review Techniques
• Definition: In PERT activities are shown as a network of precedence
relationships using activity-on-arrow network construction
– Multiple time estimates
– Probabilistic activity times
USED IN : Project management - for non-repetitive jobs (research and
development work), where the time and cost estimates tend to be
quite uncertain. This technique uses probabilistic time estimates.

Originated by H.L.Gantt in 1918
Gantt chart
Advantages
- Gantt charts are quite commonly
used. They provide an easy graphical
representation of when activities
(might) take place.
Limitations
- Do not clearly indicate details
regarding the progress of activities
- Do not give a clear indication of
interrelation ship between the
separate activities

CPM/PERT
These deficiencies can be eliminated to a large extent by showing the
interdependence of various activities by means of connecting arrows
called network technique.
• Overtime CPM and PERT became one technique
• ADVANTAGES:
– Precedence relationships
– large projects
– more efficient

NETWORK TECHNIQUES
PERT CPM
-Program Evaluation and
Review Technique
- developed by the US
Navy with Booz
Hamilton Lockheed
- on the Polaris
Missile/Submarine
program 1958
Critical Path Method
Developed by El Dupont
for Chemical Plant
Shutdown Project- about
same time as PERT
Both use same calculations, almost similar
Main difference is probabilistic and deterministic in time estimation
Gantt Chart also used in scheduling

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BENEFITS OFCPM / PERT NETWORK
Consistent framework for planning, scheduling,
monitoring, and controlling project.
• Shows interdependence of all tasks, work packages,
and work units.
• Helps proper communications between departments
and functions.
• Determines expected project completion date.
• Identifies so-called critical activities, which can delay
the project completion time.

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• Identified activities with slacks that can be
delayed for specified periods without penalty, or
from which resources may be temporarily
borrowed
• Determines the dates on which tasks may be
started or must be started if the project is to stay in
schedule.
• Shows which tasks must be coordinated to avoid
resource or timing conflicts.
• Shows which tasks may run in parallel to meet
project completion date
BENEFITS OFCPM / PERT NETWORK (cont.)

Questions Answered by CPM & PERT
• Completion date?
• On Schedule?
• Within Budget?
• Critical Activities?
• How can the project be finished early at the least cost?

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Example of Simple Network –
Survey

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DEFINITION OF TERMS IN A NETWORK
• Activity : any portions of project (tasks) which required
by project, uses up resource and consumes
time – may involve labor, paper work,
contractual negotiations, machinery operations
Activity on Arrow (AOA) showed as arrow, AON
– Activity on Node
• Event : beginning or ending points of one or more
activities, instantaneous point in time, also
called ‘nodes’
• Network : Combination of all project activities and the events
ACTIVITY
PRECEEDING SUCCESSOR
EVENT

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Emphasis on Logic in Network Construction
• Construction of network should be based on logical or
technical dependencies among activities
• Example - before activity ‘Approve Drawing’ can be
started the activity ‘Prepare Drawing’ must be
completed

Activity on Node & Activity on Arrow
Activity on Node
- A completion of an activity is
represented by a node
Activity on Arrow
- An arrow represents a task,
while a node is the completion
of a task
- Arrows represent order of events

Activity Slack
Each event has two important times associated with it :
- Earliest time , Te , which is a calendar time when a event can occur when all
the predecessor events completed at the earliest possible times
- Latest time , TL , which is the latest time the event can occur with out
delaying the subsequent events and completion of project.
• Difference between the latest time and the earliest time of an event is the
slack time for that event
Positive slack : Slack is the amount of time an event can be delayed without
delaying the project completion

Critical Path
• Is that the sequence of activities and events where there is no “slack” i.e..
Zero slack
• Longest path through a network
• minimum project completion time

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Example 1- A simple network
Consider the list of four activities for making a simple product:
Activity Description Immediate
predecessors
A Buy Plastic Body -
B Design Component -
C Make Component B
D Assemble product A,C
Immediate predecessors for a particular activity are the activities
that, when completed, enable the start of the activity in question.

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Sequence of activities
• Can start work on activities A and B anytime, since
neither of these activities depends upon the
completion of prior activities.
• Activity C cannot be started until activity B has been
completed
• Activity D cannot be started until both activities A and
C have been completed.
• The graphical representation (next slide) is referred to
as the PERT/CPM network

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Network of Four Activities
1 3 4
2
A
B C
D
Arcs indicate project activities
Nodes correspond to the beginning
and ending of activities

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Example 2
Develop the network for a project with following activities and
immediate predecessors:
Activity Immediate
predecessors
A -
B -
C B
D A, C
E C
F C
G D,E,F
Try to do for the first five (A,B,C,D,E) activities

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Network of first five activities
1 3 4
2
A
B
C
D
5
E
We need to introduce
a dummy activity

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•Note how the network correctly identifies D, E, and F as the
immediate predecessors for activity G.
•Dummy activities is used to identify precedence relationships
correctly and to eliminate possible confusion of two or more
activities having the same starting and ending nodes
•Dummy activities have no resources (time, labor, machinery, etc) –
purpose is to PRESERVE LOGIC of the network
Network of Seven Activities
1 3 4
2
A
B
C
D
5
E
7
6
F
G
dummy

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1 1
2 2
3 3
4
a d
b e
c f
a d
b
e
f
c
WRONG!!! RIGHT!!!
a precedes d.
a and b precede e,
b and c precede f (a does not precede f)

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Scheduling with activity time
Activity Immediate Completion
predecessors Time (week)
A - 5
B - 6
C A 4
D A 3
E A 1
F E 4
G D,F 14
H B,C 12
I G,H 2
Total …… 51
This information indicates that the total time required to complete
activities is 51 weeks. However, we can see from the network that several
of the activities can be conducted simultaneously (A and B, for example).

Activity Relationships
Activity Relationship
AOA AON
Figure 4.1

S precedes T, which precedes U.
AOA AON
1 2
S
3
T
4
U
S T U
Figure 4.1

S and T must be completed before U can be started.
AOA AON
S
T
U
1
2
3
T
S
4
U
Figure 4.1

T and U cannot begin until S has been completed.
AOA AON
T
U
S
3
4
1
T
U
2
S
Figure 4.1

U and V cannot begin until both S and T have been completed.
AOA AON
1
2
4
5
U
V
S
T 3
S
T
U
V
Figure 4.1

U cannot begin until both S and T have been completed; V cannot
begin until T has been completed.
AOA AON
S
T
U
V
1 3
Dummy
5
2 4 6
S U
T V
Figure 4.1

T and U cannot begin until S has been completed; V cannot begin
until both T and U have been completed.
AOA AON
1 2 4
3
S T
5
V
U
Dummy
S T V
U
Figure 4.1

project network

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