Precedence Diagramming Method
“Precedence Diagramming Method” is a tool/technique for the process “Sequence Activities”.
The precedence diagramming method (PDM) is a technique used for constructing a schedule model in which activities are represented by nodes and are graphically linked by one or more logical relationships to show the sequence in which the activities are to be performed. Activity-on-node (AON) is one method of representing a precedence diagram. This is the method used by most project management software packages.
PDM includes four types of dependencies or logical relationships. A predecessor activity is an activity that logically comes before a dependent activity in a schedule. A successor activity is a dependent activity that logically
comes after another activity in a schedule. These relationships are defined below and are illustrated in Figure 6-9: – Finish-to-start (FS). A logical relationship in which a successor activity cannot start until a predecessor activity has finished. Example: The awards ceremony (successor) cannot start until the race (predecessor)
has finished.
– Finish-to-finish (FF). A logical relationship in which a successor activity cannot finish until a predecessor activity has finished. Example: Writing a document (predecessor) is required to finish before editing the
document (successor) can finish.
– Start-to-start (SS). A logical relationship in which a successor activity cannot start until a predecessor activity has started. Example: Level concrete (successor) cannot begin until pour foundation (predecessor)
begins.
– Start-to-finish (SF). A logical relationship in which a successor activity cannot finish until a predecessor activity has started. Example: The first security guard shift (successor) cannot finish until the second security guard shift (predecessor) starts.
In PDM, finish-to-start is the most commonly used type of precedence relationship. The start-to-finish relationship is very rarely used but is included to present a complete list of the PDM relationship types.
Activity A Activity B Activity A Activity A Activity B Activity B Activity A Activity B Finish to Start (FS) Start to Finish (SF) Start to Start (SS) Finish to Finish (FF) Figure 6-9. Precedence Diagramming Method (PDM) Relationship Types
This definition was found in the PMBOK V5
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