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Gantt Charts
An Introduction


Prof. David Bernstein
James Madison University

Computer Science Department
bernstdh@jmu.edu

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Background
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  • 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
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The Input Data

images/pert-example_times-and-dependencies.gif
Visualization
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  • 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.)
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Adding Task 1

images/gantt-example_task-1.gif
An Example (cont.)
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Adding Task 2

images/gantt-example_task-2.gif
An Example (cont.)
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Adding Tasks 3 and 4

images/gantt-example_task-3-4.gif
An Example (cont.)
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Adding Task 5

images/gantt-example_task-5.gif
An Example (cont.)
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All Tasks

images/gantt-example_task-all.gif
Finding the Critical Tasks
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  • 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.)
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Critical Tasks

images/gantt-example_critical-tasks.gif
An Example (cont.)
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Slack

images/gantt-example_slack.gif
Automated Tools
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One Particular Tool

images/gantt-example.gif
Automated Tools (cont.)
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  • 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
There's Always More to Learn
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