Provided & Required Interfaces
Both Interface Blocks and Interfaces can describe the behavior of a port. According to A Practical Guide to SysML, interfaces are “redundant with the capabilities of interface blocks” but they are “retained in SysML since they are used in UML, and some methodologies may choose to use the same modeling approach in SysML and UML.” Interfaces describe provided and required behavior. Oftentimes these behaviors are services offered or needed by the block which owns the Port to which the Interfaces are allocated. Although an interface may have multiple operations defined, it is not possible to selectively assign one or more operations to a provided or required interface.
Interfaces are commonly defined in a block definition diagram. An interface can be used to “type” a port on a block, in effect, creating an interface (the general, non-SysML, meaning of the term is intended here) through which material, information, or energy can pass. How this material, information, and energy is passed is determined by the operations defined by the interface. Provided and required interfaces assigned to a port are displayed with ball and socket notation. The provided interface appears as a stick with a ball protruding from the port and the required interface appears as a stick with a socket protruding from the port.
Provided and Required Interfaces on a BDD
A block’s internal block diagram also displays the provided and required interfaces of the block using ball and socket notation. When part properties are connected on an IBD, the connectors appear as lines from one port to another, NOT as lines from a ball to a socket.
Provided and Required Interfaces on an IBD
Although interfaces have an interesting legacy from UML, it remains to be seen whether this modeling element will be retained in future versions of SysML. Interface blocks will be included in SysML 2.0, however.
Reference:
Friedenthal, S., Moore, A., & Steiner, R. (2012) A Practical Guide to SysML. Waltham, MA: Morgan Kaufmann. pg. 165 - 167.
