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Precedence Diagramming Method
What is the precedence diagramming method? It’s a technique used for constructing a schedule model, where activities which are represented by “nodes”, and are linked by one or more logical relationships to show their sequence.
That is a bit of a mouthful, from the PMBOK guide, but what we’re saying is we’ve got our schedule, and we’ve got activities on a timeline (i.e. June, July, August) and various activities need to be done. We are looking specifically at what might precede this particular activity, or the logical relationships.
For example, what can start when this one starts? And what needs to finish before this one can finish? These are the logical relationships.
The Precedence Diagramming Method includes four types of dependencies or logical relationships. We’ve got Finish to Start, Start to Start, Finish to Finish, and Start to Finish. Let’s delve into them in a little bit more detail.
Finish to Start is where the next activity cannot start until the previous activity has finished – so it’s finish to start.
The next one we are looking at is Start to Start, and this is where the next activity cannot start until the previous activity has started – so we need a start before we can have our second start, or this second activity is dependent on the first activity starting.
Then we’ve got our Finish to Finish, where the next activity cannot finish until the first activity has finished.
And lastly we have Start to Finish this one is when the next activity cannot finish until the previous activity has started, so our second activity cannot finish until this first one has started, or it’s dependent on this one starting.
And that is the idea behind the Precedence Diagramming Method.
– David McLachlan