\tt TROLL is a language to specify information systems with dynamic behavior. Here, we elaborate on the specification of \em object aggregation in \tt TROLL. We distinguish between two kinds of aggregation, static and dynamic aggregation. Static aggregation means that the composition of objects is described using predicates over constant properties. Dynamic aggregation means that we may alter the composition of objects by invoking special operations (\em events) that are implicitly defined for each dynamic complex object. Additionally, we describe the specification of disjoint complex as a means for structuring a specification. We introduce language features to describe object aggregation and give some hints towards their semantics.