Project Management Tools: The Gantt Chart · 2020. 3. 22. · Project managers have relied on...

Software Project Management 5. Creating The Project Plan – Part III

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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


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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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Figure 3

Gantt

Chart

Example

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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. �





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


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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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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. �



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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





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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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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Science Minia University��

Table 1. Example of a Work Breakdown Structure



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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. ��





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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Table 2 Data for Estimated Durations for Tasks in Figure 1





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



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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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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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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





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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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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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. ��



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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.��





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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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/CPMTable 3 Initial Data for a Crashing Example


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Project Management Tools: PERT/CPMTable 4 Data for Crashable Days and Cost-Time Slope for a Crashing Example




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. ��



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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. ��




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Figure 4 A network diagram after the first iteration of crashing


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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.��






Figure 5 A network diagram after the second iteration of crashing


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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 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

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Project Management Tools: The Gantt Chart · 2020. 3. 22. · Project managers have relied on...

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