project management tools: the gantt chart · 2020. 3. 22. · project managers have relied on...
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Software Project Management 5. Creating The Project Plan – Part III
1/17
Prof. Moheb Ramzy Girgis
Department of Computer Science
Faculty of Science
Minia University
Software Project Management
5. Creating The Project Plan – Part III
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
Project managers utilize several tools to help manage
projects.
The project work plan, discussed previously, is a critical
element of managing projects.
In addition, graphical tools are used to understand the
relationship between project tasks and to monitor progress
on the project. The first one is Gantt chart. A Gantt chart is a horizontal bar chart that shows the
same task information as the project work plan, but in a
graphical way.
The Gantt chart can communicate the high-level status of a
project much faster and easier than the work plan.
Creating a Gantt chart is simple and can be done with a
spreadsheet package, graphics software (e.g., Microsoft
VISIO), or a project management package.�
Project Management Tools: The Gantt Chart
Software Project Management 5. Creating The Project Plan – Part III
2/17
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
First, tasks are listed as rows in the chart, and time is listed
across the top in increments based on the needs of the
projects. (See Figure 3).
A short project may be divided into hours or days, whereas
a medium-sized project may be represented in weeks or
months.
Horizontal bars are drawn to represent the duration of each
task; the bar’s beginning and end mark exactly when the
task will begin and end.
As people work on tasks, the appropriate bars are filled in
proportionately to how much of the task is finished.
Too many tasks on a Gantt chart can become confusing,
so it’s best to limit the number of tasks to around 20 to 30.
If there are more tasks, break them down into subtasks
and create Gantt charts for each level of detail.
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Project Management Tools: The Gantt Chart
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
Figure 3
Gantt
Chart
Example
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Software Project Management 5. Creating The Project Plan – Part III
3/17
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
There are many things a project manager can see by
looking quickly at a Gantt chart: See how long tasks are and how far along they are.
See which tasks are sequential, which tasks occur at the
same time, and which tasks overlap in some way.
Get a quick view of tasks that are ahead of schedule and
behind schedule by drawing a vertical line on today’s date.
If a bar is not filled in and appears to the left of the line, that
task is behind schedule.
There are a few special notations that can be placed on a
Gantt chart: Project milestones are shown by diamonds.
Arrows are drawn between the task bars to show task
dependencies.
Sometimes, the names of people assigned to each task are
listed next to the task bars to show what human resources
have been allocated to each task. �
Project Management Tools: The Gantt Chart
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
Two other graphical ways to look at the project work plan
information are: PERT (Program Evaluation and Review Technique) and CPM (Critical Path Method)
Project managers have relied on PERT/CPM techniques to
plan, schedule, and control projects for the last 60 years.
PERT was developed in the U.S. Navy. In 1957, its Special
Projects Office created the PERT chart to assist in its
Polaris nuclear submarine project.
Owing to the success of the Polaris project, PERT gained
popularity and was adopted in project-based manufacturing
organizations.
CPM had its origins in the construction industry.
Usually, project managers combine the two techniques and
use them together (known as PERT/CPM).
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Project Management Tools: PERT/CPM
Software Project Management 5. Creating The Project Plan – Part III
4/17
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
Network Diagram
The backbone of the PERT and CPM techniques is a
network diagram.
A network diagram graphically represents the relationships
between the tasks that are needed to execute and
complete a project.
Traditionally, a network diagram is composed of events (also referred to as milestones).
An event denotes reaching of a milestone or the
completion of a task.
An event does not consume resources.
In classic network diagrams, an event is represented by a
circle.
The events are connected by arrows that represent tasks.
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Project Management Tools: PERT/CPM
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
A task is the smallest unit of productive effort that can be
planned, scheduled, and controlled.
Tasks are also referred to as activities.
A task consumes resources: time, money, material,
equipment, and information.
In classic network diagrams, a task is represented by an
arrow.
In more modern network diagrams, a task is represented
by a circle or some other shape. In these diagrams, arrows
are used to represent precedence relationships.
In a diagram, the entire network is embedded between two
events: the Start event and the End event.
The Start event signifies the start of the project; the End
event signifies completion of the project.
The more modern network diagrams are referred to as
Activity-oriented network diagrams. �
Project Management Tools: PERT/CPM
Software Project Management 5. Creating The Project Plan – Part III
5/17
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
Activity-oriented network diagrams are referred to as
activity on node (AON) network diagrams or
precedence network diagrams. An AON network
diagram is depicted in Figure 1.
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Figure 1 An AON network diagram
Project Management Tools: PERT/CPM
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
Construction of a Network Diagram
Step 1: Develop the work breakdown structure (WBS) for the project.
We will use a Start-End approach to construct a network
diagram. In this approach, the steps include:
1. Enumerating all tasks that are to be performed to begin
the project
2. Enumerating all tasks that are to be performed upon
completion of the initial tasks
3. Enumerating the next level of tasks that are to be
performed
4. Iterating Step 3 until all tasks have been defined
5. A final listing of all tasks (When all tasks have been listed,
the WBS is ready.)
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Project Management Tools: PERT/CPM
Software Project Management 5. Creating The Project Plan – Part III
6/17
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
Once all tasks have been identified, we establish the
precedence relationships between the tasks in the WBS.
Remember that some tasks can be performed in parallel
with each other (concurrently), and also that some tasks
have to be performed in sequence (one after the other).
In the diagram shown in Figure 1, Module 1 and Module 2
tasks can be performed concurrently, but Integration and
Testing tasks need to be performed in sequence. In other
words, Testing can only be started after completion of the
Integration task.
As an illustration, let’s build a WBS that would generate the
network diagram shown in Figure 1. This WBS is shown in
Table 1.
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Project Management Tools: PERT/CPM
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University��
Table 1. Example of a Work Breakdown Structure
Project Management Tools: PERT/CPM
Software Project Management 5. Creating The Project Plan – Part III
7/17
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
Using the WBS in Table 1, we can draw the network
diagram shown in Figure 1.
Step 2: Estimate the Duration for Each Task
PERT recognizes the uncertainty inherent in estimation.
So, it recommends estimating three values of duration for
each task:
Optimistic time: Optimistic time (to) is the best-case-
scenario duration: an expert performs the task, all
resources are available on time, no unforeseen incidents
cause delays, etc. Optimistic time is the shortest
duration in which a task can be completed.
Pessimistic time: Pessimistic time (tp) is the worst-
case-scenario duration: a novice performs the task, all
possible delays occur, resource availability is delayed,
etc. Pessimistic time is the longest duration needed to
complete a task. ��
Project Management Tools: PERT/CPM
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
Most likely time: Most likely time (tm) is a normal-case-
scenario duration: a person with average skills performs
the operation, some delays occur, most resources are
available on time, etc. Most likely time is the duration
that will usually take place to complete a task.
From these three duration values, the expected time (te) can be computed using the formula:
te = (to + 4tm + tp)/6
Table 2 shows an example of computations of the
expected times for the tasks of the network diagram shown
in Figure 1.
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Project Management Tools: PERT/CPM
Software Project Management 5. Creating The Project Plan – Part III
8/17
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University��
Table 2 Data for Estimated Durations for Tasks in Figure 1
Project Management Tools: PERT/CPM
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
Now let’s calculate the duration required to complete the
project. We compute this value using the expected time of
each task (te). We do this from the network diagram shown in
Figure 1. We place the values for Start and Finish near the
node (as shown in Figure 2).
��Figure 2 Forward pass: a network diagram with earliest Start and Finish
values for each task
Project Management Tools: PERT/CPM
Software Project Management 5. Creating The Project Plan – Part III
9/17
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
In Figure 2:
ES represents the Earliest Start time, which signifies the
day on which the task can begin, as counted from the first
day on which the project began.
EF represents Earliest Finish time and signifies the day on
which the task can earliest finish, as calculated from the
day on which the project began.
ES is computed as the Earliest Finish day of the preceding
task. For example, the design task of Module 1 can be started
on day 6. Day 6 is the day on which the preceding
Requirements analysis task for Module 1 finishes.
Now consider the Integration task, which has two preceding
tasks: the construction of Module 1 and the construction of
Module 2. Construction of Module 1 finishes on day 27,
whereas the construction of Module 2 finishes on day 26. The
Integration task can therefore start only on day 27.
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Project Management Tools: PERT/CPM
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
Therefore,
the rule for computing the ES for a task is the last finish
time of all of its predecessor tasks;
the rule for computing the EF for a task is simply the ES of
the task plus its duration.
The method of computing project duration that we have just
described is referred to as forward pass or the earliest time computation.
Based on this computation, the End task finishes on day 38,
which is the earliest duration for the project completion.
Now we compute the durations for the tasks by beginning
from the End task backward until we reach the Start task.
We compute the latest times for all the tasks coming
backward from the End task to the Start task.
This method is referred to as backward pass (shown in
Figure 3).
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Project Management Tools: PERT/CPM
Software Project Management 5. Creating The Project Plan – Part III
10/17
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
In Figure 3:
LS represents the Latest Start time for a task.
LS is the time at which a task must start so that the
successor task will not be delayed.
LF represents the Latest Finish time for the task.
��Figure 3 Backward pass: a network diagram with the Latest Start and Finish
values for each task
Project Management Tools: PERT/CPM
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
To compute the latest times, we begin at the End task and
work backward.
So, for the Testing task, the LF should be day 38 so that
the End task is not delayed. The LS for the Testing task is
(LF – duration) or day 34. [LS = LF – Duration]
We work backward in this manner and compute the latest
times for all tasks.
The difference between the earliest time and the latest time
for a task is known as slack or float. For example, for the Design task of Module 2, the ES is 5 and
the LS is 6 (alternately, EF is 12 and LF is 13).
Therefore, the slack for that task is 1 (or 13 – 12).
Slack is the amount of time by which the task could be
delayed without delaying its successor tasks.
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Project Management Tools: PERT/CPM
Software Project Management 5. Creating The Project Plan – Part III
11/17
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
The critical path method (CPM) It allows the identification of the critical path in the network.
The critical path is the longest path from the Start task to the
End task. It shows all the tasks that must be completed on
schedule for the project as a whole to finish on schedule.
The tasks on the critical path are called critical tasks.
Critical tasks are vital to the timely completion of the project.
Any delay in completing a critical task will directly and
proportionately delay the project’s completion.
The critical path can be derived by identifying the critical tasks from the network graph.
It is easy to identify the critical tasks. They are those tasks
that have no slack.
In a network diagram, all critical tasks are normally connected
by a red arrow.
In Figure 3, the critical tasks are connected by a thicker line.
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Project Management Tools: PERT/CPM
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
To arrive at the duration of the project, simply sum up the
duration of each of the tasks on the critical path.
Another way to derive the critical path is to first trace all of the
parallel paths on the network diagram from the Start task to
the End task and compute their durations.
Notice in Figure 3 that there are two paths: Path 1 and Path 2. Path 1 is Start–Requirements Analysis for Module 1–Design
of Module 1–Construction of Module 1–Integration–Testing–
End. The duration of this path is 38 days.
Path 2 is Start–Requirements Analysis for Module 2–Design
of Module 2–Construction of Module 2–Integration–Testing–
End. The duration of this path is 37 days.
As mentioned above, the critical path in a network is the path
that has the longest duration from the Start task to the End
task.
Clearly, Path 1 has longer duration. Path 1 is therefore the
critical path in Figure 3. ��
Project Management Tools: PERT/CPM
Software Project Management 5. Creating The Project Plan – Part III
12/17
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
Crashing The Project CPM treats the duration of tasks as deterministic.
Deterministic tasks are those tasks whose duration is
known with certainty.
CPM uses a single time estimate for each task. CPM
assumes the possibility, however, that by pumping in more
resources, the duration of the tasks can be reduced, within
certain predefined limits, so that the total duration of the
project can be reduced.
This aspect of pumping in more resources to reduce the
duration of tasks, and thereby reducing the total duration of
a project, is known as crashing the project. Crashing is the systematic reduction of the duration of an
entire project, with the least possible increase in the cost of
the project.��
Project Management Tools: PERT/CPM
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
Why would we need to resort to crashing the project?
Often the project completion date arrived at by our
computations and the completion date demanded by the
client are not the same.
If the completion date demanded by the client is later than
our date, all is well. But if the date demanded by the client
occurs before our date, we are faced with a difficult
situation.
Crashing can help us try to reduce the initial project
completion date to meet client demands.
Each task is associated with two sets of values: (normal duration and normal cost) and (crash duration and crash cost).
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Project Management Tools: PERT/CPM
Software Project Management 5. Creating The Project Plan – Part III
13/17
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
For example, say the Design task of Module 1 has a
normal duration of 5 days, with an associated normal cost
of 1000. The task’s crash duration is 3 days and its crash
cost is 1500.
The task’s crash cost per day = (1500 – 1000) � 2 = 250,
a value that is known as cost-time slope.
Let’s now look at an example of crashing using the project
depicted in Figure 3.
The initial data for crashing is shown in Table 3. Using
these data, we can compute the number of crashable days
and the cost-time slope for each task, which is shown in
Table 4.
Crashing is an iterative process because the process takes
a number of iterations to achieve the objective.
In this example, for a better understanding of the process,
let’s crash the project to its minimum possible duration. ��
Project Management Tools: PERT/CPM
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University��
Project Management Tools: PERT/CPMTable 3 Initial Data for a Crashing Example
Software Project Management 5. Creating The Project Plan – Part III
14/17
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University��
Project Management Tools: PERT/CPMTable 4 Data for Crashable Days and Cost-Time Slope for a Crashing Example
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
In the first iteration, we will have two paths: Path 1 is 1–2–3–4–8–9–10, with duration of 38 days;
Path 2 is 1–5–6–7–8–9–10, with duration of 37 days.
Thus, the critical path is 1–2–3–4–8–9–10.
To reduce the duration, we crash critical tasks.
So, we first consider the task that has the least cost-time
slope for crashing.
We see in Table 4 that Task 4 (Construction of Module 1)
has the least cost-time slope — 1000 per day. So, we will
select this task for crashing.
Next, we decide how much duration do we crash?
We select duration such that the present critical path will
not become shorter than any other path in the network
diagram after crashing.
We already know that the difference between the two paths
is 1 day, so we can crash Task 4 for 1 day. ��
Project Management Tools: PERT/CPM
Software Project Management 5. Creating The Project Plan – Part III
15/17
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
From our discussion, we can now formulate the rules for
crashing in the first iteration:1. Select the task on the critical path that has the least cost-
time slope.
2. Select the duration such that the duration of the critical path
after crashing is not less than any other paths in the network
diagram.
Next, we redraw the network diagram using this new
information.
The new network diagram drawn after the first iteration of
crashing is shown in Figure 4.
Now, let’s carry out the second iteration.
As you can see from the new network diagram in Figure 4, we
now have two critical paths.
When there is more than one critical path in a network
diagram, select tasks that are common to all of the critical
paths. ��
Project Management Tools: PERT/CPM
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University�
Project Management Tools: PERT/CPM
Figure 4 A network diagram after the first iteration of crashing
Software Project Management 5. Creating The Project Plan – Part III
16/17
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
In Figure 4, there are two such tasks: Integration and Testing.
When there are multiple candidate tasks for crashing, we
select the one with the least cost-time slope.
In our example, there is only one task that can be crashed:
Integration, which can be crashed by 2 days at an extra cost
of 4000.
But before crashing, a question needs to be answered: “Will
full crashing (i.e., reducing the duration of the Integration task
fully to its minimum duration) reduce the entire project
duration in the same linear amount? In this case: “Yes.”
So we can crash the Integration task fully and redraw the
network diagram. Now, project duration is reduced to 35 days.
The revised network diagram is shown in Figure 5.
If further crashing is possible, do it and compute the critical
path once more, and continue to iterate until the desired
duration is reached.��
Project Management Tools: PERT/CPM
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University��
Project Management Tools: PERT/CPM
Figure 5 A network diagram after the second iteration of crashing
Software Project Management 5. Creating The Project Plan – Part III
17/17
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
Summary of project crashing steps:1. Crashing is a systematic process to reduce the duration of a
project with minimum increase in project cost.
2. Before attempting crashing, set an objective for the reduction of
project duration (or set the maximum permissible increase in
project cost).
3. Crashing is iterated until the objective is met.
4. In any iteration, the rules for selecting the candidate tasks for
crashing are:
a. If there are multiple critical paths, then select the tasks that are
common to all critical paths.
b. Otherwise, select the tasks that have the least cost-time slope.
5. Crash the selected tasks and recalculate the critical paths.
6. Check to see if the objectives have been met in terms of duration
and cost.
7. If the objectives are met, redraw/update the network diagram and
end the process. If the objectives are not met, reiterate Steps 4 to
6 until the objectives are met. ��
Project Management Tools: PERT/CPM
Software Project Management - Prof. Moheb Ramzy
Girgis Dept. of Computer Science - Faculty of
Science Minia University
Project management software packages like Microsoft Project enable the project manager to input the work
plan once and then display the information in many
different formats. You can toggle between the work
plan, a Gantt chart, and PERT/CPM, depending on
your project management needs.
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Project Management Packages