Network plan and Gantt chart

In short: A network plan shows the dependencies between the activities of a project and determines the critical path. A Gantt chart shows the activities as bars on a time axis.

In more detail: In the network plan each activity has a duration, a predecessor and points in time: earliest start (FAZ), earliest end (FEZ), latest start (SAZ), latest end (SEZ). The difference is the float. Activities without float lie on the critical path: if one is delayed, the entire project is delayed.

In Depth

Forward pass: FEZ = FAZ + duration. The FAZ of an activity is the largest FEZ of its predecessors. Backward pass: SAZ = SEZ − duration. The SEZ is the smallest SAZ of the successors. Total float: SAZ − FAZ. Free float: FAZ of the successor − FEZ of the activity.

Example: A (3 days) → B (4) and C (2) → D (2). The path A→B→D takes 9 days, A→C→D 7 days. Critical path: A–B–D, C has 2 days of float.

• Milestone: important point in time without duration (for example acceptance).
• Gantt: good for communication, shows dependencies less well.
• Tools: project management software, spreadsheets.
• Agile: agile methods plan in short iterations.

See also: Lastenheft and Pflichtenheft (requirement specifications), Agile methods: Scrum and Kanban