Precedence Diagram Method

Precedence Diagram Method (PDM) is a visual representation technique that depicts the activities involved in a project. PDM was developed subsequent to the PERT/CPM techniques and its function is to permit a more accurate depiction of relationships among various activities.

There are four (4) types of dependencies that you need to be aware of before creating a Precedence Diagram.

• Finish-Start: In this dependency, an activity cannot start before a previous activity has ended. This is the most commonly used dependency.
• Start-Start: In this dependency, there is a defined relationship between the start of activities.
• Finish-Finish: In this dependency, there is a defined relationship between the end dates of activities.
• Start-Finish: In this dependency, there is a defined relationship between the start of one activity and the end date of a successor activity. This dependency is rarely used.

Network scheduling techniques provide managers with a powerful tool for scheduling and controlling their programs/projects. In general, they permit the graphic portrayal of project activities and relationships among the activities. This provides the basis for determining the project’s critical path, predicting shortages, and identifying possible reallocation of resources to solve problems. Through the use of readily available software, network schedules are fairly easy to update and rework, thus providing managers with current program/project status information and control over activities and schedules.

The precedence diagram method is a tool for scheduling activities in a project plan. It is a method of constructing a project schedule network diagram that uses boxes, referred to as nodes, to represent activities and connects them with arrows that show the dependencies.

• Critical tasks, noncritical tasks, and slack time
• Shows the relationship of the tasks to each other
• Allows for what-if, worst-case, best-case and most likely scenario

Key elements include determining predecessors and defining attributes such as early start date, late start date, early finish date, late finish date, duration and WBS reference.