Refactoring collections in OCL

The current OCL 2.4 specification organizes collections in one abstract class, Collection(T), and four concrete subclasses, namely Set(T), Bag(T), Sequence(T), and OrderedSet(T) depending on whether the collection elements are ordered or not, and whether duplicated elements are allowed or not. These four classes provide a clear and useful partition of the whole collections space, covering all relevant aspects. However, the specification of the operations associated with these classes is rather unwieldy and inefficient in the current standard: it contains duplicated descriptions, missing operations and unspecified details. In this paper, we analyze the problems with such specifications, and propose an alternative specification that avoids duplication and missing details based on the introduction of the appropriate intermediate abstract classes that capture the common features of interest of each kind of collection.