Precedence Diagram Method in Scheduling

Precedence Diagram Method

Precedence Diagram Method
Precedence Diagram Method

The Precedence Diagram Method (PDM) is a visual technique used for preparing a work schedule in which activities are represented by nodes or boxes and linked by one or more dependencies to show the order in which the activities are to be performed.

Basically, while preparing a work schedule we use two common network diagrams:

Arrow Diagramming Method (ADM)
Precedence Diagram Method or Activity on Node diagram or (PDM)

The Precedence Diagram Method (PDM)



In Precedence Diagram Method (PDM), nodes or boxes are used to represent activities and arrows show the relationships.
While constructing a schedule activity dependencies must be determined. In this determination process Predecessor and Successor activities must be specified.
Predecessor Activity: A predecessor activity is an activity whose start or finish controls start or finish of another activity
Successor Activity: A successor activity is an activity whose start or finish is controlled by start or finish of another activity

Dependencies in the Precedence Diagram Method (PDM)

There are four types of relationships in The Precedence Diagram Method between the activities.

Finish to Start: A successor activity cannot start until a predecessor activity has finished

Finish to Start
Finish to Start

Start to Start: A successor activity cannot start until a predecessor activity has started

Start to Start
Start to Start

Finish to Finish: A successor activity cannot finish until a predecessor activity has finished

Finish to Finish
Finish to Finish

Start to Finish: A successor activity cannot finish until a predecessor activity has started

Start to Finish
Start to Finish

Finish to Start is the most common dependency in network diagrams. Depending on the type of dependency a lead or lag may be used to represent the nature of activity relationships.

Lead is the time that an activity precedes the start or finish of its successor.
Lag is the time that an activity is delayed from the the start or finish of its predecessor.

Summary



Network scheduling techniques are used in order to determine the project’s critical path and identify relocation of resources to meet the project time management requirements. By the help of softwares it is very easy to construct the schedule network diagrams and analyze the critical paths effectively. Also network diagramming softwares such as Primavera P6 or Microsoft Project Professional enable project managers, planning engineers and schedulers to make updates and detailed analyzes quickly.

See Also

Arrow Diagramming Method in Scheduling

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