Slides by: Ms. Shree Jaswal
Introduction
developing the project schedule
Scheduling Charts
logic diagrams and network (AOA,AON)
critical path
calendar scheduling and time based network
management schedule reserve
PDM network,
PERT
CPM
Resource loading, resource leveling
allocating scarce resources to projects and several projects
Goldratt’s critical chain.
Chapter 4 Slides by: Ms. Shree Jaswal 2
Textbook:
* Chp 7: The Project's Schedule and budget
Reference Books:
#1 Chp 7: Network Scheduling and PDM
#1 Chp 8:PERT, CPM, Resource Allocation and GERT
#1 Chp 9: Cost estimating and budgeting
#1 Chp 10:Managing risks in projects
#2 Chp 8:Project Activity Scheduling
Note:* Textbook: "Information Technology Project Management" Jack T.
Marchewka
#1 Reference book: "Project Management for business and Technology"
John M. Nicholas
#2 Reference book: "Project Management" Jack R. Meredith
Chapter 4 Slides by: Ms. Shree Jaswal 3
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Activity definition
Activity sequencing
Activity duration estimation
Schedule development
Schedule control
Chapter 4 Slides by: Ms. Shree Jaswal 5
Project Management Tools
Gantt Charts
Project Network Diagrams
Activity on the Node (AON), Activity on arrow (AOA)
Critical Path Analysis
Pert
Precedence Diagramming Method (PDM)
Chapter 4 Slides by: Ms. Shree Jaswal 6
Simplest and most commonly used scheduling
technique
The chart consists of horizontal scale divided into
time units-days, weeks or months and vertical
scale showing project work elements.
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Advantages:
Gives a clear pictorial model of the project.
Simplicity for the planner and the user.
Easy to construct & understand.
Is a means for assessing the status of individual work elements and the project as a whole.
It can be used as Expense Charts
1.for labor planning
2.resource allocation
3.budgeting
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Drawbacks:
It does not explicitly show interrelationships
among work elements.
Gantt charts are often maintained manually. This
is easy task in small projects, but is burdensome
and a disadvantage in large projects; it causes
apathy and results in charts becoming outdated.
Chapter 4 Slides by: Ms. Shree Jaswal 13
Activity Start time Duration
A 0 5
B 6 3
C 7 4
D 8 5
14Chapter 4 Slides by: Ms. Shree Jaswal
0 6 12 18 24 30
Gantt charts
Time
Activitie
s
15Chapter 4 Slides by: Ms. Shree Jaswal
Suppose C & D must start only after activity B is
completed.
16Chapter 4 Slides by: Ms. Shree Jaswal
0 6 12 18 24 30
Gantt charts
Time
Activitie
s
17Chapter 4 Slides by: Ms. Shree Jaswal
Gantt charts don’t explicitly show task
relationships
don’t show impact of delays or shifting
resources well
network models clearly show
interdependencies
18Chapter 4 Slides by: Ms. Shree Jaswal
network of relationships
elements & relationships (sequence)
this is ACTIVITY-ON-NODE
can have ACTIVITY-ON-ARC
research
what’s
been done
research
what needs
doing pick
final
topicinternet
research
write print
19Chapter 4 Slides by: Ms. Shree Jaswal
Activity on node diagrams
A,6 B,9
20Chapter 4 Slides by: Ms. Shree Jaswal
Activity on arc or arrow
21 3
21Chapter 4 Slides by: Ms. Shree Jaswal
Activity Duration Immediate Predecessor
A 6 _
B 9 A
C 8 A
D 4 B,C
E 6 B,C
Duration is given in weeks
22Chapter 4 Slides by: Ms. Shree Jaswal
AON diagram corresponding to data in prev table
Critical path A-B-E:21 weeks
Start A,6
B,9 D,4
C,8 E,6
Finish
23Chapter 4 Slides by: Ms. Shree Jaswal
Activity on arc or arrow
Same example on AON network
1 2
A,12
24Chapter 4 Slides by: Ms. Shree Jaswal
Activity Immediate Predecessors Duration
A _ 6
B A 9
C A 8
D B,C 4
E B 6
F D,E 6
Duration is in days
25Chapter 4 Slides by: Ms. Shree Jaswal
1 2
26Chapter 4 Slides by: Ms. Shree Jaswal
Activity Immediate Predecessors Duration
A _ 6
B A 9
C A 8
D B,C 4
E B 6
F D,E 6
Duration is in days
27Chapter 4 Slides by: Ms. Shree Jaswal
1 2
4
3
28Chapter 4 Slides by: Ms. Shree Jaswal
Activity Immediate Predecessors Duration
A _ 6
B A 9
C A 8
D B,C 4
E B 6
F D,E 6
Duration is in days
29Chapter 4 Slides by: Ms. Shree Jaswal
1 2
4
3
55 6
30Chapter 4 Slides by: Ms. Shree Jaswal
Activity Immediate Predecessors Duration
A _ 6
B A 9
C A 8
D B,C 4
E B 6
F D,E 6
Duration is in days
31Chapter 4 Slides by: Ms. Shree Jaswal
1 2
4
3
5 6
7
32Chapter 4 Slides by: Ms. Shree Jaswal
Activity Immediate Predecessors Duration
A _ 6
B A 9
C A 8
D B,C 4
E B 6
F D,E 6
Duration is in days
33Chapter 4 Slides by: Ms. Shree Jaswal
3-5, 4-5, 7-8,6-8 are dummy activities
1 2
4
3
5 6
7
8 9
34Chapter 4 Slides by: Ms. Shree Jaswal
Dummy activities are used in AOA diagrams in case a node has more than one immediate predecessor.
In previous example:Activity Immediate Predecessors Duration
D B,C 4
F D,E 6
To represent activities D & F we use dummy activities
Chapter 4 Slides by: Ms. Shree Jaswal 35
ACTIVITY PREDECESSOR IMMEDIATE PRED: REDUNDANT PRED:
A --
B A A
C A A
D A,B,C B,C A
E A,B,C,D D A,B,C
F A,B,C B,C A
REDUNDANT ACTIVITY
36Chapter 4 Slides by: Ms. Shree Jaswal
It is only essential to know the immediate
predecessor of a node while constructing a
network.
All the predecessors except the immediate
predecessors of a node are redundant
predecessors( activities).
37Chapter 4 Slides by: Ms. Shree Jaswal
AON n/ws
There are no dummy activities
They are simpler
They are easier to construct.
38Chapter 4 Slides by: Ms. Shree Jaswal
AOA n/w’s
AOA method used just as often, probably because it was developed first and is better suited for PERT procedures
The PERT model places emphasis on events and in the AOA method events are specifically designated by nodes.
AOA diagrams use line segments to represent flow of work and time, it is easy to construct schedules that are similar in appearance to Gantt charts but incorporate advantage of networks
39Chapter 4 Slides by: Ms. Shree Jaswal
Most software packages create AOA n/w’s
that look similar to Gantt charts.
In particular it is best to select one form of
technique., AON or AOA, and stick to it.
40Chapter 4 Slides by: Ms. Shree Jaswal
The longest path from the origin node to the terminal
node
Gives the expected project duration (Te)
One project can have more than one CP
Shortening activities on CP (critical activities) will
help reduce the project duration
Shortening activities NOT on CP has no effect on
project duration
Delay in any activities on CP will result in delay of
project completion
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Start A,6
B,9 D,4
C,8 E,6
Finish
Critical path A-B-E:21 weeks
Activity,
duratio
n
predece
ssor
A,6 -
B,9 A
C,8 A
D,4 B,C
E,6 B,C
42Chapter 4 Slides by: Ms. Shree Jaswal
Specifies when at the earliest the activities can be
performed.
ES & EF are computed by taking a FORWARD pass
through the network
When an activity has several predecessors, its ES is
the MAXIMUM of all EF of predecessors
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Latest allowable times that the activity can be started
and finished without delaying the completion of the
project.
LS & LF are computed by taking a REVERSE pass
through the network. LS for the last activity (Ts) is
taken same as the EF for that activity (Te); larger value
can be selected if project does not have to be
completed by EF.
When an activity with multiple paths leading back,
backward path with MINIMUM of all LS is selected.
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Eg:
activity duration__predecessor
A requirements analysis 3 weeks -
B programming 7 weeks A
C get hardware 1 week A
D train users 3 weeks B, C
45Chapter 4 Slides by: Ms. Shree Jaswal
Critical path is: A-B-D 13 weeks
1 2
3
4
5 6
46Chapter 4 Slides by: Ms. Shree Jaswal
Total slack= LS-ES or LF-EF
Total slack of all activities along critical path
is zero.
Hence delaying any of these activities will
delay the project.
47Chapter 4 Slides by: Ms. Shree Jaswal
Free Slack= ES( earliest successor)- EF
In the eg, activity C has a free slack of 6
weeks( 10-4=6)
Free slack indicated the amount by which
activity can be delayed without affecting the
start of its successor activity.
48Chapter 4 Slides by: Ms. Shree Jaswal
can have more than one critical path
activity duration predecessor
A requirements analysis 3 weeks -
B programming 7 weeks A
C get hardware 7 weeks A
D train users 3 weeks B, C
critical paths A-B-D
A-C-D
both with duration of 13 weeks
49Chapter 4 Slides by: Ms. Shree Jaswal
After a project network has been created
and finalized the resulting schedule times
should be converted into a calendar schedule
plan
Calendar schedule plan expresses the
schedule in terms of calendar dates
Chapter 4 Slides by: Ms. Shree Jaswal 50
To complete the calendar schedule, the
network is converted into a time-based
network
Time based n/w’s have advantages of both
Gantt charts and networks because they
show the calendar schedules as well as
relationships among activities.
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The Te first computed from the n/w is usually not the duration specified as the contractual completion time.
A Management schedule reserve is established by setting the required target time Ts at some amount greater than the time of the final schedule event Te.
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The schedule reserve and a management
budget reserve comprise a “safety buffer” that
the project manager can use to overcome
problems or delays that threaten project
performance
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Need for PDM: “Predecessor - Sucessor” type of networks
assume a “strict” sequential relationship between activities
They do not provide for tasks that can be started when their predecessors are only “partially” complete
PDM allows multiple relationships between activities Finish-to-Start (FS)
Start-to-Start (SS)
Start-to-Finish (SF)
Finish-to-Finish (FF)
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Finish-to-Start (FS)
The start of the Activity B can occur n days, at the earliest after the finish of Activity A
Start-to-Start (SS)
The start of Activity B can occur n days, at the earliest after the start of Activity A
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Start-to-Finish (SF)
The finish of Activity B must occur n days,
at the latest after the start of Activity A
Finish-to-Finish (FF)
The finish of Activity B will occur in n
days, at the latest after Activity A finishes
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PDM: RelationshipsA 15
PlasterWall
B 10Tear-down scaffolding
FS=5
A
FS=5
B
A 15Furniture move in
B 10Peoplemove in
SS=5
A
SS=5
B
A 15Test
new system
B 10Phase outold system
SF=20
A
SF=20
B
A 15Lay
asphalt
B 10Paint
parking linesFF=5
A
FF=5
B
60Chapter 4 Slides by: Ms.
Shree Jaswal
The two most commonly used methods for project planning and scheduling are:
Program Evaluation and Review Technique (PERT)
Critical Path method (CPM)
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Program Evaluation & Review Technique (PERT)
The Framework for PERT and CPM
There are six steps which are common to both
1. Define the Project and all of it’s significant activities or tasks.
2. Develop the relationships among the activities. Decide which activities must precede and which must follow others.
Chapter 4 Slides by: Ms. Shree Jaswal 62
3. Draw the "Network" connecting all the activities. Each Activity should have unique event numbers. Dummy arrows are used where required to avoid giving the same numbering to two activities
4.Assign time and/or cost estimates to each activity
5. Compute the longest time path through the network. This is called the critical path.
6.Use the Network to help plan, schedule, monitor and control the project.
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PERT was developed for application in projects where there is uncertainty associated with the duration and nature of activities.
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reflects PROBABILISTIC nature of durations
assumes BETA distribution
same as CPM except THREE duration estimates
optimistic
most likely
pessimistic
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Three time estimates :
The Optimistic (a) The minimum time in which the activity can be
completed
The Most Likely (m) Completion time having the highest probability
(normal time to complete the job)
The Pessimistic (b)
The longest time an activity could take to complete
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a = optimistic duration estimatem = most likely duration estimateb = pessimistic duration estimate
Mean or expected time for completion of an activity , te is given byte = (a + 4m + b)/6
Variance, V is given byV = sqr((b-a)/6)
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The expected time Te , represents the point on distribution where there is a 50-50 chance that the activity will be completed earlier or later than it.
a=3,b=5,c=13
Te= (3+4(5)+13)/6= 6 days
Variance is the measure of variability in the activity completion time:
V=sqr((13-3)/6)=sqr(1.67)= 2.78
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The larger V, the less reliable Te, and the higher the likelihood that the activity will be completed much earlier or much later than Te.
More dispersed the distribution and greater the chance that the actual time will be significantly different from the expected time Te
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Probability of finishing by a target completion
date
The expected duration of a project - Te, is the
sum of expected activity times along the
critical path.
Te = ∑ te
The variation in the project duration
distribution is computed as the sum of the
variances of the activity durations along the
critical path
Vp = ∑ V
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Now, although the project is estimated to be completed
within 29 weeks (Te=29) our Project Director would
like to know what is the probability that the project
might be completed within 27 weeks (i.e.Ts=27 or Due
Date or D=27).
For this calculation, we use the formula for calculating
Z, the number of standard deviations that D is away
from Te.
Z =(Ts-Te)/ √ Vp
Chapter 4 Slides by: Ms. Shree Jaswal 73
Thus, Z=(27-29)/ √ 6 = -0.82
After referring to table for Z values for normal
distribution,
X1=-0.8,X2=-1.0,Y1=0.212,Y2=0.159
Now, using the formula,
Y=Y1+[(Y1-Y2)/X1-X2)]*(X-X1), we get
Y=0.2067=0.21(approx)
Therefore, probability is 21% to finish project
in 27 days
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For above example to find out what is the date
when 95% of project will have been
completed…..
Again using the table and interpolating,
probability of 0.95 has Z value=1.645
Thus,1.645=(Ts-29)/ √ 6
So, Ts=33.03 days (highly likely)
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Putting too much emphasis on the critical
path can lead managers to ignore other paths
that are near-critical or have large variances,
and which themselves could easily become
critical
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Monte Carlo simulation is a procedure that takes into account the effects of near critical paths becoming critical.
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Need to have considerable amount of
historical data to make time estimates
PERT gives overly optimistic results.
Beta distribution gives large errors in
estimating Te.
Most of the errors in Te come from faulty
time estimates not Beta distribution.
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Although PERT and CPM employ networks and use the concept of critical path, the methods have two points of divergence.
CPM is a deterministic approach.CPM includes a mathematical procedure
for estimating the trade-off between project duration and cost.
CPM features analysis of reallocation of resources from one job to another to achieve the greatest reduction in project duration for the least cost.
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BASIS FOR
COMPARISONPERT CPM
Meaning PERT is a project
management
technique, used to
manage uncertain
activities of a
project.
CPM is a statistical
technique of project
management that
manages well defined
activities of a
project.
What is it? A technique of
planning and control
of time.
A method to control
cost and time.
Orientation Event-oriented Activity-oriented
Evolution Evolved as Research
& Development
project
Evolved as
Construction project
Chapter 4 Slides by: Ms. Shree Jaswal 82
BASIS FOR
COMPARISONPERT CPM
Model Probabilistic Model Deterministic Model
Focuses on Time Time-cost trade-off
Estimates Three time estimates One time estimate
Appropriate for High precision time
estimate
Reasonable time
estimate
Critical and Non-
critical activities
No differentiation Differentiated
Suitable for Research and
Development Project
Non-research
projects like civil
construction, ship
building etc.
Crashing concept Not Applicable Applicable