An instance of ISpan represents a span constraint. A span constraint between an interval variable a and a set of interval variables {b1,...,bn} states that interval a spans over all present intervals from the set {b1,...,bn}. That is: interval a starts together with the first present interval from {b1,...,bn} and ends together with the last one. Interval a is absent if and only if all intervals in {b1,...,bn} are absent.

You must add this constraint to a model and extract the model to an algorithm in order for it to be taken into account.

For more information on the span constraint, see the concept Constraints on Groups of Interval Variables in the C++ Reference Manual.