Collection is an abstract type, containing these three subtypes: Set, Bag and Sequence. Each subtype has its own graphical representation, which is listed underneath:

A Set contains an assumption of objects without repetition, whereas a Bag includes an assumption of objects, which may occur several times. The Sequence type finally is a Bag with an order of each element in the list.

Simple navigations lead to a Set, as seen before. Combined navigations may result in a Bag and with the operation sortedBy you are able to produce a Sequence.