Primavera P6 supports 2 types of constraints; hard constraints and soft constraints.
In Primavera P6, “Mandatory” constraints are hard constraints. Hard constraints stand out because they can break relationships. An activity that has a Mandatory Start or Finish date becomes fixed to that date. Relationships to that activity are ignored – the activity will not move even if its predecessors push it out.
All of P6’s other constraints are considered soft constraints. A soft constraint is one that P6 will try to adhere to, but relationships take priority, and may result in the constraint not being met.
Michael,
Nice, quick and to the point article. I really think constraints are overlooked by a lot of new schedulers and sometimes can be applied incorrectly. The Start (or Finish) on or Before constraint is misunderstood and misused by many schedulers and needs to be thought of in a “contractual” use for the most part. Also, I’m not a fan of Mandatory Constraints because, as you said, they override logic. Again, good article and keep up the good work!
Sean
Michael,
Thank you for that. Best explaination I’ve ever seen, and I’ve been at it since the blue screen days.
Enjoy your articles, keep up the good work.
J
Michael,
Short and brief, so worthy to read.
Very usuful article like all other articles!
Cheers
thanks for concise answer but HAVING SAID THAT DO YOU MEAN THAT CONSTRAINTS OTHER THAN WITH WORD “Manadatory” are soft constraints and p6 has only two hard constraints manadatory start and manstory finish.
please confirm
thanks
Azhar Islam
Azhar – yes, what you have written is correct.
A Hard Constraint and a Soft Constraint in the context of a Goal Programming Model are constraints only and hence, they have no impact on the objective function.
Is it true?
Hey Sam,
We’re discussing constraints in the context of project scheduling. I do not know if what you’ve written is true.