Activity-On-Arrow (AOA)

Activity-on-Arrow (AOA) represents an activity using an arrow of a particular length, thus allowing beginners to conceptualize and understand activity on the network easily. An AOA network can be relatively smoothly translated to a time-scaled network that helps users to understand the execution time of each activity schematically, by making the length of a narrow proportional to the duration of the activity.

Activity-On-Arrow (AOA) is a project management term that refers to a specific method of representing project activities within a project management diagram, often called an Arrow Diagramming Method (ADM). It is an example of a network diagram, which is used to visualize the workflow and the chronological order of tasks in a project.

However, the AOA method has a serious disadvantage in identifying and applying dummies. Depending on the network condition, a complex analysis may be required for applying dummies. Activity-on-Arrow is a dummy with zero time and no resource requirement; no actual work is performed in a dummy. Activity-on-Arrow (AOA) is a tool that can be used to create the intended work logically or to assign a task to a dummy.

Purpose and Role

AOA is primarily used for scheduling (time management) and visually represents the project activities. In an AOA diagram, each arrow represents a project activity, and the nodes (points) where arrows start and end represent the beginning and end of the activity, respectively. The direction of the arrow indicates the sequence of tasks.


The essential components of an AOA diagram are:

  1. Activity: An action/task that needs to be accomplished within a defined period.
  2. Event (Node): It is represented by a circle and marks the start or end of activities.
  3. Dummy Activity: A dummy activity, often represented by a dotted arrow, shows dependencies between tasks but consumes no resources or time.


AOA diagrams are crucial in project management as they help visualize the flow of activities, identify dependencies between tasks, manage resources efficiently, and estimate the shortest project duration (critical path).


The AOA diagram technique was developed in the late 1950s as part of the Program Evaluation and Review Technique (PERT) by the U.S. Navy. It has been used widely in project management, especially in construction and defense industries.


  1. Helps in visualizing the project timeline and the flow of tasks.
  2. Identifies the critical path in a project schedule.
  3. Assists in predicting the project completion time.


  1. Can become very complex for large projects with numerous tasks.
  2. Does not clearly show dependencies between parallel tasks.


For instance, consider a simple project consisting of three tasks: Design, Build, and Test. An arrow will represent each of these tasks in an AOA diagram. The start of the 'Design' arrow represents the beginning of the design task. Once the 'Design' task is completed, it enables the start of the 'Build' task, represented by the node at the end of the 'Design' arrow and the start of the 'Build' arrow. Similarly, the 'Test' task can begin after completing the 'Build' task.

Semantically related keywords

  1. Critical Path Method (CPM): A step-by-step project management technique for process planning that defines critical and non-critical tasks.
  2. Program Evaluation and Review Technique (PERT): A statistical tool used in project management to analyze and represent the tasks involved in completing a project.
  3. Activity-On-Node (AON): A method which differs from AOA as it denotes tasks on nodes instead of arrows.
  4. Gantt Chart: A horizontal bar chart used in project management to visually represent a project plan over time.
  5. Project Management: The practice of initiating, planning, executing, controlling, and closing the work of a team to achieve specific goals and meet specific success criteria at the specified time.

See Also