What is a Project Network Diagram?

Project Network Diagram

This article extends my previous articles about Project Dependencies – What are Project Dependencies and 4 Types of Project Dependencies. I have written this post to further discuss some other aspects of Project Dependencies.

project network diagram

This article discusses about diagrammatic representation of Project Schedule and Project Dependencies. Specifically this article talks about Project Network Diagrams. You can use Project Network Diagrams to diagrammatically represent Project Schedule. It is one of the popular methods to draw Project Schedule. Project Network Diagrams are also called Project Schedule Network Diagrams or simply Network Diagrams.

There are many ways to draw Project Schedule. Project Network Diagrams is one of the ways to draw Project Schedule. Some of the other popular diagramming techniques for representing Project Schedule are:

  • Bar Charts (populary known as Gantt Charts)
  • Milestone Charts
  • Project Calendars

Project Network Diagrams also can be drawn in many ways. These include:

  • Precedence Diagramming Method (PDM)
  • Arrow Diagramming Method (ADM)
  • Conditional Diagramming Methods

Out of these PDM is most popular. It is also called Activity on Node (AON) method. PDM used by most of the modern Software Scheduling Tools. Let us discuss PDM in detail.

PDM Concepts

Predecessor Activity – It is simply called as a Predecessor. A Predecessor Activity logically comes before the dependent activity in a Project Network Diagram.

Successor Activity – It is simply called as a Successor. A Successor Activity is the dependent activity. It logically comes after another activity (Predecessor) in a Project Network Diagram.

Node – All the activities (Predecessors and Successors) in a Project Network Diagram are represented on a Node. Usually a Node is drawn as a Rectangle.

Milestones – Milestones are also represented as Nodes in a Project Network Diagram. Usually a Milestone is drawn as a small Circle. Milestones can also become a Predecessor or a Successor.

Arrow – Dependencies in a Project Network Diagram are drawn as Arrows. Two related Activities are separated by a unidirectional Arrow. Predecessors are drawn towards Arrow Tail while Successors are drawn towards Arrow Head.

Subnetwork – It is simply called as a Subnet. Subnetwork is a subdivision or part of a complete Project Network Diagram.

Dependencies – A Successor (Dependent Node) can have more than one Predecessor. Similarly a Predecessor can have more than one Successor.

PDM Diagram Example

The figure drawn below depicts a sample Project Network Diagram. It is drawn using PDM technique.


precedence diagramming method

Click to Enlarge

  • There are 3 activities – A, B and C
  • There are 2 Milestones –  S and F
  • A has only 1 Successor – Activity B
  • B has only 1 Predecessor – Activity A
  • C is neither related to A nor to B
  • Planned duration of each activity is mentioned in their respective Nodes

PDM Relationships

PDM includes 4 types of logical relationships. I have explained these in separate articles.

PDM also supports two Modifiers – Leads and Lags. These Modifiers change the nature of the logical relationships.

You can also look at Max Wideman’s Glossary for complete set of definitions.

You can also look at some of my other articles on Precedence Diagramming Method

Precedence Diagramming method is a long concept. I have split it into small articles to give more clarity. Please leave a comment is you have a question and I will be happy to answer.

Praveen Malik, PMP is a certified Project Management Professional (PMP®) with a rich 20+ years of experience. He is a leading Project Management Instructor and Consultant. He regularly conducts Project Management workshops in India & abroad.

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