PDM vs AOA-Difference between PDM and AOA network diagram methods

This page compares PDM method vs AOA method and mentions difference between PDM(Precedence Diagram Method) and AOA(Activity On Arrow) network diagram methods. Both PDM and AOA are used in project schedule or time planning.

There are two types of network diagrams.
•  Activity on Arrow diagram or AOA or Arrow Diagram
•  Activity on Node diagram or Precedence diagram method(PDM)

difference between PDM and AOA

As mentioned in the figure-1, CPM/CPA(Critical PAth Method/Critical Path Analysis) and PERT(Program Evaluation and Review Technique) fall under Arror network Diagram. PDM falls under Activity Network diagram or AON.

PDM-Precedance Diagram Method


As mentioned in fig-2 in PDM or Precedence Diagram Method nodes or boxes are used to represent activities. Arrows show activity dependencies as depicted. There are four types of dependencies between the activities.

Finish to Start:An activity must finish before the successor activity can start.
Start to Start:An activity must start before the successor activity can start
Finish to Finish:An activity must finish before the successor activity can finish
Start to Finish:An activity must start before the successor activity can finish.This type is rarely used.

AOA-Activity On Arrow


In the AOA or Activity On Arrow network diagram, the arrows are used to represent activities. The nodes represent activity dependencies. Any activity coming into a node is a predecessor to any activity leaving the node.

This method uses only finish to start relationship between activities. This may use dummy activities are inserted just to show dependencies between activities. They do not need work or take any time.

As shown in the fig-3, there are two ways we can denote activity on arrow(AOA) activity. Either the name will be on arrow as shown in fig-3 left side or activity will be named as shown in the fig-3 right side. This method requires two letter identifiers to name a single activity (e.g. A-B).

Useful PMP Related Links

Project management professional,PMP, READ MORE.
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PMP Training Institutes, READ MORE.
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