Activity-on-node is a project management term that refers to a precedence diagramming method which uses boxes to denote schedule activities. These various boxes or “nodes” are connected from beginning to end with arrows to depict a logical progression of the dependencies between the schedule activities. Each node is coded with a letter or number that correlates to an activity on the project schedule.
Typically, an activity-on-node diagram will be designed to show which activities must be completed in order for other activities to commence. This is referred to as “finish-to-start” precedence – meaning one activity must be finished before the next one can start. In the diagram below, activities A and D must be done so that activity E can begin. It is also possible to create other variations of this type of diagram. For example, a “start-to-start” diagram is one in which a predecessor activity must simply be started rather than fully completed in order for the successor activity to be initiated.
An activity-on-node diagram can be used to provide a visual representation of the network logic of an entire project schedule. Or, it can be used for any smaller section of the schedule that lends itself to being represented as having a defined beginning and end. To keep the logic in the diagram simple, it may be most effective to include only critical path schedule activities. The planned start date of each node may also be listed in the diagram legend in accordance with the project management timeline.