Precedence Diagramming Method (PDM)
The Precedence Diagramming Method (PDM) is a technique used to construct a schedule model in which activities are represented by nodes and are graphically linked by logical relationships to show the sequence of activities.
Explanation
PDM, also known as Activity-on-Node (AON), is the standard method used in modern project management to create schedule network diagrams. In PDM, each activity is represented as a box (node) and arrows between boxes show the dependencies. This is different from the older Activity-on-Arrow (AOA) method, which is rarely used today.
PDM supports four types of logical relationships between activities: Finish-to-Start (FS), where the successor cannot start until the predecessor finishes; Start-to-Start (SS), where the successor cannot start until the predecessor starts; Finish-to-Finish (FF), where the successor cannot finish until the predecessor finishes; and Start-to-Finish (SF), where the successor cannot finish until the predecessor starts. Finish-to-Start is by far the most commonly used relationship type.
PDM also accommodates leads (acceleration of the successor) and lags (delay of the successor) to more precisely model the timing between dependent activities. The resulting network diagram is the foundation for critical path analysis and schedule development.
Key Points
- •Also known as Activity-on-Node (AON)
- •Activities are represented as nodes (boxes) with arrows showing dependencies
- •Supports four relationship types: FS, SS, FF, and SF
- •Foundation for critical path analysis and schedule modeling
Exam Tip
Finish-to-Start (FS) is the most commonly used and default dependency type in PDM. If no relationship type is specified on the exam, assume FS.
Frequently Asked Questions
Related Topics
Sequence Activities
Sequence Activities is the process of identifying and documenting relationships among the project activities.
Finish-to-Start (FS) Dependency
A Finish-to-Start (FS) dependency is a logical relationship in which a successor activity cannot start until a predecessor activity has finished.
Start-to-Start (SS) Dependency
A Start-to-Start (SS) dependency is a logical relationship in which a successor activity cannot start until a predecessor activity has started.
Finish-to-Finish (FF) Dependency
A Finish-to-Finish (FF) dependency is a logical relationship in which a successor activity cannot finish until a predecessor activity has finished.
Start-to-Finish (SF) Dependency
A Start-to-Finish (SF) dependency is a logical relationship in which a successor activity cannot finish until a predecessor activity has started.
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