Precedence constraints between interval variables
Precedence constraints are
common scheduling constraints used to restrict the relative position
of interval variables in a solution.
For example a precedence constraint can model the fact that an activity a must end before activity b starts (optionally with some minimum delay z). If one or both or the interval variables of the precedence constraint is absent, then the precedence is systematically considered to be true; therefore it does not impact the schedule.
More formally, the semantics of the relation TC(
, 
, z) on a pair of fixed intervals , and for a value z depending on the constraint
type TC is given in the following table.
For syntax and examples, see the following functions described in the OPL Language Quick Reference. Note that none of these constraints may be used in a meta-constraint.