This section describes two constraints over groups of intervals. Their main purpose is to allow hierarchical creation of the model by "encapsulating" a group of interval variables by one "high level" interval. Here is an informal definition of these constraints:

• Span constraint. The constraint span(a, ) states that the interval a spans over all present intervals from the set . In other words, interval a starts together with the first present interval from and ends together with the last one.
• Alternative constraint. The constraint alternative(a, ) models an exclusive alternative between . If interval a is present then exactly one of intervals is present and a starts and ends together with this chosen one. The alternative constraint can also specify a non-negative integer cardinality c, alternative(a, , c), in this case, not 1, but c interval variables will be selected from the set and those c selected intervals will have to start and end together with interval variable a.