Interface: a collection of operations used to specify a
service of an abstraction. Each operation will have
pre-conditions and post-conditions. Also there will be
invariants unaffected by each operation. OCL can be used to
specify the semantics of interfaces. State machines may be used
to determine legal partial ordering of an interface's
operations. Collaborations will determine the expected
behaviour of an interface. Interface implemented by a
class. The objects of an implementing class will have methods
that provide the operations in the interface. An implementing class
may realize more than one interface. Also one or more
interfaces of a class may be used by different roles which will
have some of the interface operations. Different roles correspond to
different selection of interfaces supported by the class. There may
be many implementations of the same interface. Objects use interfaces
which have been implemented. Dependency relationship between the
interface user object and the interface. <<interface>>
stereotyped class with operation used shown explicitly instead of
lollipop icon. Generalisation / specialisation diagram
with <<interface>> stereotyped class is used to include
interface hierarchy.