Project computing and Management PM 216 3.pptx

PROJECT SCHEDULING
TECHNIQUES
1

Scheduling Techniques
1. Network Diagrams
• ADM-Arrow Diagram Method
• CPM – Critical Path Method
• PERT-Program Evaluation and Review
Techniques
2. Bar Charts
• Gantt Chart
• Milestone Chart
2

Network Diagrams
• A network diagram is defined as a flow chart that
includes all of the project elements and how they
relate to one another.
• Network diagrams show the order in which
activities should be scheduled to address logical
relationships between these activities
• Developed in the 1950’s
3

• It is widely used because it is easy to read and
• not only depicts the sequence of activities in
the project,
• but also shows parallel activities and the links
between each activity.
4

Why Network diagram?
• Define the project's path
• Determine the sequence of tasks to be completed
• Look at the relationship between activities
• Determine the dependencies
• Set up simultaneous tasks

• Monitor your project by establishing benchmarks,
milestones, or deliverables —
• these are markers to determine whether your
project is on, ahead of, or behind schedule
• Make adjustments as tasks are completed
• Take a broad look at the project path and clearly
see the relationships and dependencies between
task
6

Requirements of Network Diagram
method
• Project Scope Statement
• Work Breakdown Structure (WBS
• Historical Project Information
• WBS Dictionary
• Resource Calendars
7

Network Diagrams format
• Two classic formats
– AOA: Activity on Arrow
– AON: Activity on Node
• Each task labeled with
• Identifier (usually a letter/code)
• Duration (in std. unit like days)
• There are other variations of labeling
• There is 1 start & 1 end event
• Time goes from left to right
8

Activity on Arrow(AOA)
• AOA consists of
• Circles representing Events
–Such as ‘start’ or ‘end’ of a given task
• Lines representing Tasks
–Thing being done ‘Build UI’
• a.k.a. Arrow Diagramming Method (ADM)
9

Activity on node(AON)
• AON
• Tasks on Nodes
–Nodes can be circles or rectangles (usually
latter)
–Task information written on node
• Arrows are dependencies between tasks
• a.k.a. Precedence Diagramming Method (PDM)
10

ARROW DIAGRAM METHOD
(ADM)
• ADM is constructed in terms of activities and events
• An activity is represented by an ARROW while an
event by a NODE
• The activity name or code is marked on top of the
arrow and this makes the method to be “Activity on
Arrow (AOA)”
i j
Node (Event)
Arc (Activity)
aij
12

5
• The Tail of an Arrow marks the beginning of the
activity while the Head mark the ending, the
length of an Arrow and its compass have n
significance
• An Event marks the Beginning or ending of the
activity and it occurs when all the activities
leading to it are completed
A
This event will occur when the
congested activities on arrows are
finished
2
10
13

1
3
1 2
4
5
6 7
Activity
Event Node
14

Rules of drawing an ADM
1.An activity is marked by a Tail and a Head events
• The Tail event is called i event while the node head
is j event. This makes an activity to be marked
numerically by pair of events called i and j.
• Example activity A(i,j) whereby if i =1 and j=2 it
will be named A (1,2)
i j
1 2
15

2. Each event is marked by an existing number and the
number at the head of the arrow is greater than the
number at the tail
3. No more than one activity can have the same i,j as
shown below. That the same number for the tail or head
It is not accepted to have only two activities connecting to
each other
1 2
1 2
16

• There should be an introduction of another activity
called DUMMY activity to connect the two activities
• This is an imaginary activity which does not consume
time or resources and is represented by a dashed Arrow
as shown below
• A dummy used to separate tasks that would otherwise
start and stop with the same events or to show logical
sequence
1 3
2 Dummy activity
17

4. There are no loops or backward flow sequences as
shown below.
5.All nodes except the start and end nodes must be
connected by at least on predecessor and on successor
activity
1 3
2
18

Structure of event
• EOT-Earliest Occurrence Time
• LOT-Late occurrence time
1
LOT
EOT
Event
number
19

CRITICAL PATH METHOD
(CPM)
• A CP in PM is the longest sequence of activities
that must be finished on time in order for the
entire project to be complete.
• Any delays in critical tasks will delay the rest of the
project.
• CPM revolves around discovering the most
important tasks in the project timeline, identifying
task dependencies, and calculating task durations.
21

• The critical path method (CPM) is a technique
where you identify tasks that are necessary for
project completion
• This is a method that calculates the longest
path of planned activities to the end of the
project
• The method consider the earliest and latest
date that each activity can start and finish
without extending the project.
• Any activity delay on the critical path impacts
the planned project completion date.

• By looking at a network diagram, project managers
can determine when they have float or slack,
• which is the amount of time that any given schedule
activity can be delayed without causing a delay to the
– start date of subsequent activities (free float) or
– to the project completion date (total float).
• In this method Non-Critical Path tasks can start
earlier or later without impacting completion date of
the project
23

Benefits of CPM
i. Provides a graphical view of the project.
ii. Predicts the time required to complete the project.
iii. Shows which activities are critical to maintaining
the schedule and which are not.
iv. Improves future planning: CPM can be used to
compare expectations with actual progress.
v. Facilitates more effective resource management
vi. Helps avoid bottlenecks: Bottlenecks in projects can
result in lost valuable time.
24

CP Format
• CPM models the activities and events of a
project as a network.
• Activities are depicted as nodes on the
network and events that signify the beginning
or ending of activities are depicted as arcs or
lines between the nodes.
• The following is an example of a CPM
network diagram:
25

Steps on developing CPM
1. Identify/specify individual activities.
2. Determine the sequence of those activities.
3. Draw a network diagram.
4. Estimate the completion time for each activity.
5. Identify the critical path (longest path through the
network)
6. Update the CPM diagram as the project progresses
27

1. Identify/Specify individual activities
• From the work breakdown structure, a listing can be
made of all the activities in the project.
• This listing can be used as the basis for adding
sequence and duration information in later steps.
• Activities obtained from WBS are listed in a table by
giving them letters or symbols to represent them e.g.
A,B,C,D,E………
28

• For example, let’s say the marketing team is
producing a new interactive blog post.
• Here are some tasks that might be in the work
breakdown structure

• Once you have a high-level idea of everything
that needs to be done, you can start
identifying task dependencies.

2. Determine the sequence of those
activities/Identify dependecies.
• Based on your work breakdown structure,
determine the tasks that are dependent on one
another.
• Here are the task dependencies based on the
example above: if at all
• Task B is dependent on A
• Task C is dependent on B
• Tasks C and D can run in parallel
• Task E is dependent on D
• Task F is dependent on C, D, and E
32

Other Example of Activities Sequence
33

3. Draw a network diagram.
• The next step is to turn the work breakdown
structure into a network diagram, which is a
flowchart displaying the chronology of activities.
• Create a box for each task and use arrows to
depict task dependencies.
• You’ll add other time-bound components to the
network diagram until you have the general
project schedule figured out
• Task to be carried out in the class…..
35

4. Estimate the completion time for each activity.
• To calculate the critical path, the longest sequence of
critical tasks, you first need to estimate the duration of
each activity.
• The time required to complete each activity can be
estimated using past experience or the estimates of
knowledgeable persons.
• CPM is a deterministic model that does not take into
account variation in the completion time, so only one
number is used for an activity's time estimate.
• See a table below…
39

Assembly for an Automatic Storage / Retrieval
System
Activity Description
Immediate
Predecessors
Duration
A Construct storage racks - 10
B Assemble bins - 8
C Construct base A 5
D Build tracks - 4
E Construct Crane D 12
F Assemble storage container E 5
G Install motors E 7
H Install gear trains C, E 4
I Connect computer controls H, B, F 10
J Test system I 5
40

Determining Starting and Ending Times
• Early start (ES)
• Early Finish (EF)
• Late start (LS)
• Late finish (LF)
• Float time (Slack)
All these times are characteristics of an activity and are
included in a NODE
48

NODE Content
Early start Early Finish
Late Start Late Finish
Activity Name
Duration
Slack
49

1. Calculate Early Start & Early Finish dates
(FORWARD PASS)
2. Calculate Late Start & Late Finish dates
(BACKWARD PASS)
3. Calculate TOTAL FLOAT for each activity
4. Identify activities with 0 (zero) TOTAL FLOAT
50

Forward Pass
• To determine early start (ES) and early finish (EF) times
for each task
• Work from left to right
• Adding times in each path
• Rule: when several tasks converge, the ES for the next
task is the largest of preceding EF times
52

Backward Pass
• To determine the last finish (LF) and last start (LS)
times
• Start at the end node
• Compute the bottom pair of numbers
• Subtract duration from connecting node’s earliest start
time
54

Calculating Slack or Float time
• Total Float – the amount of time a task can be delayed
without delaying the project end date.
• Using the early start (ES) and late start (LS) , Early
Finish(EF) and Late Finish(LF) can be used to determine
Slack time
Slack/Total Float = LS – ES
Or = LF – EF
57

5. Identify the critical path (longest path through
the network)
• The critical path is the path through the project network in
which none of the activities have slack, that is, the path for
which ES=LS and EF=LF for all activities in the path.
• A delay in the critical path delays the project.
• Similarly, to accelerate the project it is necessary to reduce
the total time required for the activities in the critical path.
61

Task…
• Identification of a critical path on the example
62

6. Update the CPM diagram as the project
progresses
• As the project progresses, the actual task completion
times will be known and the network diagram can be
updated to include this information.
• A new critical path may emerge, and structural changes
may be made in the network if project requirements
change
66

DRAG Time
• DRAG time is the amount of time that an activity on the
critical path is adding to the project’s duration or,
• The amount of time by which the project completion would
be pulled in by reducing a critical path activity’s duration to
zero.
• Alternatively, it is the maximum amount of time that one
can shorten the activity before it is no longer on the critical
path or before its duration becomes zero.
67

• Activities that are not on the critical path are said to
have total float or slack, i.e., the amount of time they
can slip without making the project longer.
• Conversely, only critical path activities and delays such
as lags or constraints have DRAG.
68

• If an activity on critical path has nothing in parallel,
its DRAG is equal to its duration.
• If an activity on critical path has other paths in
parallel, its DRAG is whichever is less: its duration
or the total float of the parallel activity with the least
total float
69

Example
By: Mr. Edson Baradyana (UDOM,
2018)
70

From the Network
• Activities A and E have nothing in parallel and
therefore have drags of 10 days and 20 days
respectively.
71

• Activities B and C are both parallel to F (float of
15) and H (float of 20). B has a duration of 20 and
drag of 15 (equal to F's float), while C has a
duration of only 5 days and thus drag of only 5.
72

• Activity D, with a duration of 10 days, is parallel to G
(float of 5) and H (float of 20) and therefore its drag
is equal to 5, the float of G.
73

Advantages and disadvantages of Network
diagram
• Advantages
– Show precedence well
– Reveal interdependencies not shown in other techniques
– Ability to calculate critical path
– Ability to perform “what if” exercises
• Disadvantages
– Default model assumes resources are unlimited
• You need to incorporate this yourself (Resource
Dependencies) when determining the “real” Critical
Path
– Difficult to follow on large projects
74

4 .Task Dependency Types
• Mandatory Dependencies
• “Hard logic” dependencies
• Nature of the work dictates an ordering
• Ex: Coding has to precede testing
• Ex: UI design precedes UI implementation
• Discretionary Dependencies
• “Soft logic” dependencies
• Determined by the project management team
• Process-driven
• Ex: Discretionary order of creating certain modules
75

4 .Task Dependency Types
• External Dependencies
• Outside of the project itself
• Ex: Release of 3rd
party product; contract signoff
• Ex: stakeholders, suppliers, Y2K, year end
• Resource Dependencies
• Two task rely on the same resource
• Ex: You have only one DBA but multiple DB tasks
76

Task Dependency Relationships
• Finish-to-Start (FS)
– B cannot start till A finishes
– A: Construct fence; B: Paint Fence
• Start-to-Start (SS)
– B cannot start till A starts
– A: Pour foundation; B: Level concrete
• Finish-to-Finish (FF)
– B cannot finish till A finishes
– A: Add wiring; B: Inspect electrical
• Start-to-Finish (SF)
– B cannot finish till A starts (rare)
77

78
Gantt Charts
• Gantt charts are used as a tool to monitor and
control the project progress.
• A Gantt Chart is a graphical presentation that
displays activities as follows:
–Time is measured on the horizontal axis.
–Each activity is listed on the vertical axis.
• In an earliest time Gantt chart each bar begins and
ends at the earliest start/finish the activity can take
place.

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 79

80
• Gantt chart can be used as a visual aid for tracking
the progress of project activities.
• Appropriate percentage of a bar is shaded to
document the completed work.
• The manager can easily see if the project is
progressing on schedule (with respect to the
earliest possible completion times).
Gantt Charts
Monitoring Project Progress

81
Immediate Estimated
Activity Predecessor Completion Time
A None 90
B A 15
C B 5
D G 20
E D 21
F A 25
G C,F 14
H D 28
I A 30
J D,I 45
A
90
90
B
15
F
25
I
30
105
C
5
115
G
14
129
D
20
149
E
21
H
28
J
45
194
194

82
A
90
B
15
F
25
I
30
C
5
G
14
D
20
E
21
H
28
J
45
194
194
135
Monitoring Project Progress
The shaded bars represent
completed work BY DAY 135.
Do not conclude that the
project is behind schedule.
Activity “I” has a slack and
therefore can be delayed!!!

85
• Advantages.
– Easy to construct
– Gives earliest completion date.
– Provides a schedule of earliest possible start and finish times of
activities.
• Disadvantages
– Gives only one possible schedule (earliest).
– Does not show whether the project is behind schedule.
– Does not demonstrate the effects of delays in any one activity on
the
start of another activity, thus on the project completion time.
Gantt Charts –
Advantages and Disadvantages

PERT
• The time to complete an activity is random
meaning if a given activity were done over and
over again one would expect the completion times
to be different sometimes
• The Program Evaluation and Review Technique is
a network (PERT) model that allow randomness
in activity completion times.
• It was developed in late 1950’s for the US Navy’s
Polaris missile project having thousands of
contractors with aim of reducing time and costs to
complete projects 86

Steps in PERT
• PERT planning involves the following steps
1. Identify specific activities and milestones
2. Determine proper sequence of activities
3. Construct a Network diagram
4. Estimate time required for each activity
5. Determine critical path
6. Update PERT chart as the project progress 87

NOTE:
• NOTE: All the steps are the same as CPM but
the difference is on step 4 with Estimation of
the Completion time of an Activity
88

PERT Network diagram/Chart
• PERT Network diagram is called PERT CHART
• In PERT chart activities are shown as a network
of precedence relationships using Activity-On-
Arrow (AON) network construction with
–Multiple time estimates
–Probabilistic activity times
89

By: Mr. Edson Baradyana (UDOM,
2018)
91

Time estimation in PERT
• PERT recognize that Times of completion of activities in
Project vary due to different reasons some being;
1. Skills level of people doing the activity
2. Machine variations
3. Material availability
4. Unexpected events (sickness ,natural disasters,
workers strikes, industrial accidents, employees
turnover etc. 92

3 times estimates used in PERT
• PERT uses three time estimates to calculate the time
of completion of an activity;
• Optimistic completion time
• Pessimistic completion time
• Most likely completion time
93

• Optimistic time (O) – Time required to complete an activity if
everything goes perfectly (No delay)
• Pessimistic time (P) – Time required to complete an activity if
everything that can go wrong go wrong
• Most likely time (M) – Time required to complete the activity
under normal situations
In many cases all these three times may be estimated from prior
experiences with similar activities
94

PERT Formula
• Combined 3-times are used to determine the time of
completion (Duration) for an activity using the
formula below
95

PERT advantages and disadvantages
• Advantages
– Accounts for uncertainty
• Disadvantages
– Time and labor intensive
– Assumption of unlimited resources is big issue
– Lack of functional ownership of estimates
– Mostly only used on large, complex project
96

CPM vs. PERT
• Both use Network Diagrams
• CPM: deterministic
• PERT: probabilistic
• CPM: one estimate, PERT, three estimates
• PERT is infrequently used
97

Project computing and Management PM 216 3.pptx

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