Constraints allow a CPM network to model external dependencies that are outside of the standard predecessor-successor logic. P6 allows for various types of constraints. Unfortunately, keeping track of activities with constraints can be a difficult task especially if both Primary and Secondary constraints are used.
It’s important to realize that overly assigning constraints to a CPM network works against the algorithm date calculations during the forward and backward pass. Constraints should be kept to an absolute minimum. Also Constraints should be totally understood as to exactly how they affect the Early/Late Start/Finish dates as well as the Total Float value.
Constraints allow a CPM network to model external dependencies that are outside of the standard predecessor-successor logic. P6 allows for various types of constraints. Unfortunately, keeping track of activities with constraints can be a difficult task especially if both Primary and Secondary constraints are used.
In the Illustration above, the 9 possible Primary Constraints and 2 possible Secondary Constraint are listed.
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