Precedence Diagram Method in Project Management

Precedence Diagram Method in Project Management
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  • 0:05 Precedence Diagram Method
  • 1:06 Types of Dependencies…
  • 2:09 Elements of the PDM
  • 2:46 How to Build the…
  • 3:58 Why is the PDM Important?
  • 4:30 Lesson Summary
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Lesson Transcript
Instructor: Mike Miller
In this lesson, you'll learn how to explain the precedence diagram method, lay out a schedule using this method and explain the how precedence diagram method is used in project management.

Precedence Diagram Method

According to the Project Management Institute, the precedence diagram method (PDM) is a technique used for constructing a schedule in which activities are represented by nodes and linked by one or more logical relationships to show the sequence in which the activities are to be performed. This is also known as activity on the node diagrams.

The inputs that go into scheduling include scope and deliverables. A project manager should gather his team for a schedule planning meeting. During the meeting, the project manager will review scope, deliverables, and any dates of importance. The project management team will list each activity needed to complete the project.

The project manager and the project management team will also have a list of activities and milestones. Milestones are items of significance for the project. A milestone could be the first prototype rolling off the assembly line or an inspection that's tied to funding, such as a framing inspection that can be tied to a loan draw when building a house.

Types of Dependencies in the PDM

There are four common types of dependencies in the precedence diagram method. The first and most common dependency is called finish to start. This is where one activity cannot start until another finishes. The next most common dependency is known asstart to start, where an activity cannot start until another activity starts. The third most common dependency is named finish to finish, where the completion of an activity depends on another activity finishing. The final common dependency type is called start to finish and is where one activity cannot finish until another activity starts.

Each of these dependencies can be mandatory, discretionary, external, or internal. In addition, depending on the type of dependency, a lead or lag may be needed to help schedule activities. A lead, for example on a finish to start dependency, would allow an activity to start 'X' days prior to the activity completing. A lag, for example, on a start to start, on the other hand, would be starting an activity 'X' days after the predecessor starts.

Elements of the PDM

The elements of the precedence diagram method include a variety of activities, which are represented pictorially by nodes. Each node will have:

  • Early start date (ES or ESD)
  • Late start date (LD or LSD)
  • Early finish date (ED or EFD)
  • Late finish date (LD or LFD)
  • Duration (d)
  • WBS reference or description
  • Float

Here is an example of a node diagram key, which includes all the acronyms and an example of a node itself in the precedence diagram method:

Node key

node example

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