An interval sequence variable is defined on a set of interval variables {a1,...,an}. Informally speaking, the value of an interval sequence variable represents a total ordering of the interval variables {a1,...,an}. Absent interval variables are not considered in the ordering.

The sequence variable alone does not enforce any constraint on the relative position of intervals start and end points. For instance, an interval variable a could be sequenced before an interval variable b in a sequence without any impact on the relative position between the start/end points of a and b (a could still be fixed to start after the end of b). This is because different semantics can be used to define how a sequence constrains the positions of intervals. One of these semantics is implemented by the constraint INoOverlap that ensures that interval variables in the sequence do not overlap and that the order of the sequence corresponds with the order of the interval start and end points.

Each interval variable in a sequence variable can be given a non-negative integer type which is local to the sequence variable. This integer type is used by some constraints on the sequence variable (see INoOverlap). The notion of type allows grouping the set of intervals according to this type value.

For more information on interval sequence variables, see the concept Interval Variables Sequencing in the C++ Reference Manual.