Gantt Charts

Gantt Charts
An Introduction

Prof. David Bernstein
James Madison University

Computer Science Department

bernstdh@jmu.edu

Background

The Question:
- How long will it take to complete a specific (design or implementation) project (or part of a project)?
A Review of the Issues:
- Units Matter
- Task Details Matter
- Task Dependencies Matter
- Personnel Capabilities Matter
Gantt Charts:
- First developed in the early 1900s

An Example

The Input Data

Visualization

Dimensions:
- Time increases from left to right
- Tasks are added from top to bottom
Tasks:
- Represented as rectangles
- The left side is positioned at the earliest possible initiation time
- The horizontal extent corresponds to its task time (i.e., duration) duration
- The vertical extent is arbitrary
Dependencies:
- Represented as arrows

An Example (cont.)

Adding Task 1

An Example (cont.)

Adding Task 2

An Example (cont.)

Adding Tasks 3 and 4

An Example (cont.)

Adding Task 5

An Example (cont.)

All Tasks

Finding the Critical Tasks

The Process:
- Start with the task with the latest completion time
- Work backwards and find the predecessor that has the latest completion time
- Continue
The Example
- Start with task 14
- 14 has two predecessors, 12 and 13, and 12 has the later completion time
- 12 has two predecessors, 10 and 11, and 10 has the later completion time

An Example (cont.)

Critical Tasks

An Example (cont.)

Slack

Automated Tools

One Particular Tool

Automated Tools (cont.)

Consider Task 12:
- It is red so is on the critical path (so can't slip)
- It isn't completed until day 23
Consider Task 9:
- It is blue so is NOT on the critical path (so can slip)
- It isn't completed until day 14
- The black line representing slack is 5 long