Compare and contrast activity-on-node versus activity-on-arrow project networks?

Answer 1

A project network illustrates the relationships between activities (or tasks) in the project. Showing the activities as nodes or on arrows between event nodes are two main ways to draw those relationships.

With activities on arrow (AOA) diagrams, you are limited to showing only the finish-to-start relationships - that is, the arrow can represent only that the activity spans the time from the event at the start of the arrow to the event at the end. As well, "dummy" activities have to be added to show some of the more complex relationships and dependencies between activities. These diagrams came into use in the 1950's, but are now falling into disuse.

Activity on node (AON) diagrams place the activity on the node, and the interconnection arrows illustrate the dependencies between the activities. There are more flexible and can show all of the major types of relationships. Since the activity is on a node, the emphasis (and more data) usually can be placed on the activity.

AOA diagrams emphasize the milestones (events); AON networks emphasize the tasks.