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Definition: This is a method of constructing a project network diagram that uses boxes or rectangles (nodes) to represent the activities and connects them with arrows that show the dependencies. This technique is also called activity-on-node (AON) and is the method used by most project management software packages. PDM can be done manually or on a computer. It includes four types of dependencies or precedence relationships:
• Finish-to-start—the initiation of the work of the successor depends upon the completion of the work of the predecessor
• Finish-to-finish—the completion of the work of the successor depends upon the completion of the work of the predecessor
• Start-to-start—the initiation of the work of the successor depends upon the initiation of the work of the predecessor
• Start-to-finish—the completion of the successor is dependent upon the initiation of the predecessor.
In PDM, finish-to-start is the most commonly used type of logical relationship. Start-to-finish relationships are rarely used, and then typically only by professional scheduling engineers. Using start-tostart, finish-to-finish, or start-to-finish relationships with project management software can produce unexpected results, since these types of relationships have not been consistently implemented.

Acceptance Level:  Generally accepted
Alternative or Related Terms: Activity-on-Node (AON), PERT Chart
Application Areas/Intended Uses: PDM is a tool or technique in activity sequencing.
Chief Advantages: Helps identify and document logical relationships
between activities in a project.
Additional Reading:
Project Management: A Systems Approach to Planning, Scheduling and Controlling, Sixth Edition. Harold Kerzner. John Wiley & Sons, Inc., 1998.