Precedence Diagramming Method (PDM)

PDM is used to construct the schedule model based on the logical relationship of the activities within the project. One of the methods used under diagramming method is Activity on Node or AON. The activities are represented within the nodes and the arrow shows the relationship between the activities. One more method under diagramming method is Activity on Arrow (AOA). Here the arrow represents the activity.

There are four types of relationships used when constructing schedule model using Precedence Diagramming Method.

Finish to Start (FS): Starting of an activity depends on the finishing of the previous activity. For example starting of the second shift depends on finishing of the first shift.

Start to Start (SS): Starting of an activity depends on the starting of the other activity. Here two activities run in parallel. For example starting of the training depends on starting of the assembly of the delegates. Here I am assuming trainer need not to wait for all the delegates to come. Even one delegate is enough to start the training.

Finish to Finish (FF): Finishing of an activity depends on finishing of the other activity. Again here two activities run in parallel. For example finishing of project closing depends on finishing of lessons learned documentation. Lessons learned activity might have started earlier itself, but by the time project closing finishes lessons learned should finish or at the same time.

Start to Finish (SF): Finishing of an activity depends on starting of the other activity. For example the finishing of first shift depends on starting of the second shift.

SF is very rarely used and FS is frequently used.

Also AOA is outdated. AOA can’t use all the four types of relationships. It can use only FS relationship whereas AON uses all the four types of relationships.

Precedence Diagramming Method technique is used under the process Sequence Activities.