Network diagram types: Activity On Node (AON) and Activity On Arrow (AOA)

There are many kinds of network diagram, but the classic ones are AON and AOA diagrams.

AOA diagram

AOA diagram is drawn using circles as the nodes , with nodes represents the beginning and ending points of  the arrows or tasks. Arrows act as activities or tasks in AOA diagram. Even though AOA is a good approach to draw a network diagram, it has its own drawbacks too. The following are the drawbacks of AOA network diagram conventions identified by Taylor (2008):

• The AOA network diagram can only show Finish to start relationships. It is not possible to show lead or lag time except by adding or subtracting time . This makes project tracking difficult.
• There are instances where "dummy activities" can occur in AOA diagram. (dummy activities are  activities which does not have duration but simply there to show dependency of one task on other task)
• AOA networks are not supported by many software tools , thus it is not not widely used.

AON diagram

AON network diagram is where circles are used to represent an activity, with arrows linking them together to show the sequence in which they are performed.The following are the advantages  of AON network diagram identified by Taylor (2008):

• AON does not have dummy activities as the arrows represents only dependencies.
• AON can accommodate any types of relationship ( Finish to Start, Finish to Finish, Start to Start, Start to finish, Lead and Lag)
• AON is  widely as it is supported by almost all the project management software tools