Activity on Arrow (A-O-A) or (A-O-L):-

1. It is composed of arrows and nodes. The arrows represent the activities and nodes represent the events.
2. Each activity carries a brief description usually printed on the logical diagram, the activity name or symbol and the time duration.
3. At present, this method seems to be the most popular method and it was the first method to be introduced, developed and computerized.
4. It is also easier to associate with time flow of activities. A major difficulty to arrow diagramming is the dummy activity.
5. Learning the usage and significance of dummies requires time and experience. It is also cumbersome to modify.

Activity on node (A-O-N) or Precedence diagrams:-

1. In A-O-N networks, the nodes represent the activities and the arrows, their interdependencies or precedence relationships.
2. Nodes are usually represented by squares or rectangles, but circles and other convenient geometrical shapes may also be used.
3. Activity number and description are written within the boxes representing the nodes.
4. Length and direction of the arrows have no significance as they indicate only the dependency of one activity on another.
5. Precedence diagramming allows more flexibility in modeling relationships than A-O-A networks, as it eliminates dummy activities.