Network Diagrams

The WBS allowed you to identify groups of activities that you need to accomplish in your project. However, the WBS does not show the dependencies or sequence between these activities. A network diagram will allow you to illustrate this. Once your network diagram is ready, only then can you realistically start determining your project’s schedule.

A Network Diagram is a visual representation of a project’s schedule. Well known complements to network diagrams include the PERT[7] and Gantt[8] charts. A network diagram in project management is useful for planning and tracking the project from beginning to finish. It represents a project’s critical path as well as the scope for the project.

A good network diagram will be a clear and concise graphic representation of a project.

There are two types of network diagrams: The Arrow Diagram and the Precedence diagram. The arrow diagram depicts nodes for events and arrows for activities. The precedence diagram depicts activities in the order they occur. If you work in IT you will most likely use the arrow diagram. 

‘A’ and ‘B’ each represents an event node. These event nodes refer to an instant when an activity is started or completed. An event node occurs only when all activities entering the node have been completed. The arrow represents the activity that takes place during the event. For example, if a task in a project were “research competition’s ad campaign,” then the event nodes would designate the start and finish of this activity whereas the arrow would designate the activity itself.

Using the arrow and node method, you can depict project dependencies. In the diagram, you see that Event C depends upon activities from Events A and B to be completed, and Event D depends upon Event C’s activities to be completed.

Dotted lines with arrows represent “dummy arrows.” Rather than depict a dependency between two items, these arrows depict a logical relationship. Dummy arrows have no duration. They do not depict an activity. Instead, they transfer logic from one event node to another.

Once the project is mapped out, you can write a key for the visual representation, listing the duration of events and activities. The network diagram will provide you and your project team with a full visual representation of your project.

---

[7] Program Evaluation Review Technique, a methodology developed by the U.S. Navy in the 1950s to manage the Polaris submarine missile program. A similar methodology, the Critical Path Method (CPM) was developed for project management in the private sector at about the same time.

[8] A Gantt chart is a horizontal bar chart developed as a production control tool in 1917 by Henry L. Gantt, an American engineer and social scientist. Frequently used in project management, a Gantt chart provides a graphical illustration of a schedule that helps to plan, coordinate, and track specific tasks in a project.