An interface is a collection of
operation signatures and/or attribute definitions that
ideally defines a cohesive set of behaviors. Interfaces
are implemented, "realized" in UML parlance, by classes
and components - to realize an interface, a class or
component must implement the operations and attributes
defined by the interface. Any given class or component
may implement zero or more interfaces, and one or more
classes or components can implement the same interface.
Figure 1. The
internals of the seminar component.
Class implementing interfaces.
Logical component architecture.
- Depict One Interface Per Port.
Ports are connection
points between a classifier and its environment that
are depicted on the side of frames as small rectangles.
Figure 1 each port has exactly
one interface, which is logically cohesive and thus does
not reveal anything about the internal design of the Seminar component.
- Depict One Port Per
Realizing Class. Another approach to organizing the
interfaces for SeminarComponent of
Figure 1 would be to have a single port
offering the Enrollment, Transcript, and
DataEntity interfaces. This would make for a
more compact diagram although contradicts
Depict One Interface Per
Port: choose an approach and stick to it.
Interfaces on the Left. In
Figure 1 the provided
interfaces are depicted using "lollipop" notation.
Interfaces on the Right. Required interfaces, such as
Student, Persistence, and XMLProcessor in
Figure 1 are depicted in
UML 2 as "sockets".
- Apply Realizes Relationships for Ports. In
Figure 1 SeminarComponent realizes the three ports on the
left of the frame and the Enrollment class
delegates to the Student port.
Reflect Implementation Language Constraints in Interface
Definitions. In Figure 2,
the interface includes a public
attribute named POID and several public
operations. Unfortunately, it could not be implemented
in Java because this language does not (yet) support
instance attributes in the definition of interfaces.
Interfaces According to Language Naming Conventions.
"Lollipop" Notation to Indicate Realization of an
Interface. As you can see in
Figure 2 there are two ways to
indicate that a class or component implements an
interface: the lollipop notation used with the Serializable interface and the realization line (the
dashed line with a closed arrowhead) used with the PersistentObject interface.
Interfaces Separately from Your Classifiers.
Not Depict the Operations and Attributes of
Interfaces in Your Classes.
Label Per Interface Connection. In
you see that the IPersistence interface is
indicated twice, once for the lollipop and once for the
- Place Interface Labels Above The Interface.