A classifier role is a model element that describes a specific role played by a classifier participating in a collaboration without specifying an exact instance of a classifier. A classifier role is neither a class nor an object. Instead, it is a model element that specifies the kind of object that must ultimately fulfill the role in the collaboration. The classifier role limits the kinds of classifier that can be used in the role by referencing a base classifier. This reference identifies the operations and attributes that an instance of a classifier will need in order to fulfill its responsibilities in the collaboration.