Lec 9 & 10 chapter 5 project scheduling

LEC 9, 10
Project Management
INTRODUCTION TO
SOFTWARE
ENGINEERING
Instructor: Maha Naeem

Work break down Structure
There are many ways of breaking down the
activities in a project, but the most usual is into:
 work packages;
 tasks;
 deliverables;
 milestones.

WBS Example
3
ABC Project
ProgrammingDesignAnalysisDefinition
Risk Analysis
Feasibility
Study
Requirements
Documentation
...
...
Level 1
Level 2
Level 3

Work Package and Tasks
A work package is a large, logically distinct section of
work:
 typically at least 12 months duration;
 may include multiple concurrent activities;
 independent of other activities;
 but may depend on, or feed into other activities;
 typically allocated to a single team.
A task is typically a much smaller piece of work:
 A part of a work package.
 typically 3–6 person months effort;
 may be dependent on other concurrent activities;
 typically allocated to a single person.

Deliverable and Milestone
A deliverable is an output of the project that can
meaningfully be assessed.
 Example
 a report (e.g., requirements spec);
 code (e.g., alpha tested product).
 Deliverables are indicators (but only indicators) of
progress.

Milestone
A milestone is a point at which progress on the
project may be assessed.
 Typically a major turning point in the project.
 Completion of an activity or deliverable (must be
measurable).
 Activities must have definite a start and stop.
 A milestone is point in time not a time period like an
activity.
 EXAMPLES:
 delivery of requirements spec
 delivery of alpha tested code

Documentation
For each work package & task, it is usual to
document:
 brief description;
 earliest start date;
 earliest end date;
 total person months effort;
 pre-requisite WPs or tasks;
 dependent WPs or tasks;
 who is responsible.

Project Scheduling
“Its All About Time”
 Scheduling:
 “what” will be done, and “who” will be working
 relative timing of tasks & time frames
 a concise description of the plan

Identifying the Activities of a Project
12
 To determine optimal schedules we need to
 Identify all the project’s activities.
 Determine the precedence relations among activities.
 Based on this information we can develop
managerial tools for project control.

Activity Network Diagrams
An activity network diagram provides a notation
for documenting
• a network of tasks needed to complete a project,
• their interdependencies
• the times required for each task.
There are a number of activity network
techniques which are similar in nature. The most
commonly used technique is CPM (Critical Path
Method).

The CPM Approach for Project
Scheduling
 The CPM approach to project scheduling
uses network presentation of the project to
 Reflect activity precedence relations
 Activity completion time
 CPM is used for scheduling activities such
that the project’s completion time is
minimized.

Example
15
Precedence/Dependences Relationships
ChartActivity Predecessor Duration
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

Immediate Predecessor
16
From the activity description
chart, we can determine
immediate predecessors for each
activity.
Activity A is an immediate predecessor
of activity B, because it must be competed
just prior to the commencement of B.
A B

Basic Terms In CPM
 ES stands for Early Start
 the earliest an activity can begin.
 AD stands for Activity Duration
 the length of time needed to complete an activity.
 EF stands for Early Finish
 the earliest an activity can finish. ES + AD
 LF stands for Late Finish
 the latest an activity can finish.
 LS stands for Late Start
 the latest an activity can begin. LF – AD

The Forward Pass
Earliest Start Time / Earliest Finish Time
 Make a forward pass through the network as follows:
 Evaluate all the activities which have no immediate
predecessors.
 The earliest start for such an activity is zero ES = 0.
 The earliest finish is the activity duration EF = Activity duration.
 Evaluate the ES of all the nodes for which EF of all the
immediate predecessor has been determined.
 ES = Max EF of all its immediate predecessors.
 EF = ES + Activity duration.
 Repeat this process until all nodes have been evaluated
 EF of the finish node is the earliest finish time of the project.

Earliest Start / Earliest Finish – Forward
Pass
A
90
B
15
C
5
F
25
I
30
G
14
D
20
E
21
H
28
J
45
90,105
90,115
90,120
105,110
110,124
115,129 129,149
149,170
149,177
120,165
149,194
170
194
A
0,90
B
I
F
C
G D
E
H
J
177
194
EARLIEST FINISH

The Backward Pass
Latest start time / Latest finish time
 Make a backward pass through the network as
follows:
 Evaluate all the activities that immediately precede the
finish node.
 The latest finish for such an activity is LF = minimal project
completion time.
 The latest start for such an activity is LS = LF - activity duration.
 Evaluate the LF of all the nodes for which LS of all the
immediate successors has been determined.
 LF = Min LS of all its immediate successors.
 LS = LF - Activity duration.
 Repeat this process backward until all nodes have been
evaluated.

B
F
C
A
I
E
DG H
H
28
166,194
J
J
45
149,194
E
21
173,194
90,105
90,115
90,120
105,110
115,129 129,149
149,170
149,177
149,194
153,173
146,166
194
129,149
0,90
129,149
D
20
129,149
129,149
129,149
129,149
129,149
129,149
129,149
G
14
115,129
I
30
119,149
29,119
C
5
110,115B
1595,110
5,95
F
25
90, 115
0,90A
90
Latest Start / Latest Finish –
Backward Pass

Slack Times
22
 Activity start time and completion time may be
delayed by planned reasons as well as by
unforeseen reasons.
 Some of these delays may affect the overall
completion date.
 To learn about the effects of these delays, we
calculate the slack time, and form the critical
path.

Slack Times
23
 Slack time is the amount of time an activity can be
delayed without delaying the project completion date,
assuming no other delays are taking place in the
project.
Slack Time = LS - ES = LF - EF

Critical activities
must be rigidly
scheduled
Activity LS - ES Slack
A 0 -0 0
B 95 - 90 5
C 110 - 105 5
D 119 - 119 0
E 173 - 149 24
F 90 - 90 0
G 115 - 115 0
H 166 - 149 17
I 119 - 90 29
J 149 - 149 0
Slack time in the Example

The Critical Path
 The critical path is a set of activities that have no
slack,
connecting the START node with the FINISH
node.
 The critical activities (activities with 0 slack) form
at least one critical path in the network.
 A critical path is the longest path in the network.
 The sum of the completion times for the activities
on the critical path is the minimal completion time
of the project.

Critical Path
 “The specific set of sequential tasks upon
which the project completion date depends”
 or “the longest full path”
 All projects have a Critical Path
 Accelerating non-critical tasks do not directly
shorten the schedule

The Critical Path
B
F
C
A
I
E
DG H
H
28
166,194
J
J
45
149,194
E
21
173,194
90,105
90,115
90,120
105,110
115,129 129,149
149,170
149,177
149,194
D
20
0,90
129,149
G
14
115,129
I
30
119,149
A
90
C
5
110,115B
15
95,110
F
25
90, 1150,90

Example
Activity Description Duration
Predecesso
r
START Kick-off meeting
A Planning 24 START
B Wireframes 16 A
C Wireframe Approval 24 B
D Design 20 C
E Design Approval 24 D
F Content Development 48 E
G Back-End Development 60 E
H Front-End Development 40 E
I Content Import 8 F, G, H
J Testing 32 G, H
K Review 40 I, J
L Launch 4 K
END L

GANTT charts
GANTT charts are a project planning tool that can
be used to represent the timing of tasks required
to complete a project.
Gantt charts are a kind of bar chart:
 time plotted on x axis
 bars on y axis for each activity.

Lec 9 & 10 chapter 5 project scheduling

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