Interfaces are two-way, consisting of requires and provides information.
An element can have multiple interfaces and multiple actors at each interface.
An architect must carefully choose what information to put in an interface specification, striking a balance between usability and modifiability. Put information in an interface document that you are willing to let people rely on. If you don't want people to rely on a piece of information, don't include it.
Follow the template given in Figure 7.1, making sure to address the needs of the interface specification's stakeholders.
In graphical depictions, show interfaces explicitly if elements have more than one interface or if you want to emphasize the existence of an interface through which interactions occur. Otherwise, interfaces can be implicit.
Many notations for interface documentation show only syntactic information. Make sure to include semantic information as well.