Aggregation is essentially the ability to embed or nest instance(s) of one type of class within another type of class.
The Cúram generator supports two types of aggregation relationships: one-to-one and one-to-many. One-to-one aggregation has the effect of embedding a single instance of one class within another. One-to-many aggregation has the effect of embedding a sequence of one class within another.
The main use for aggregation in the generator is to represent sequences in the input meta-model.