In UML diagrams, a connector is a line that represents a relationship in a model. When you model the internal structure of a classifier, you can use a connector to indicate a link between two or more instances of a part or a port. The connector defines the relationship between the objects or instances that are bound to roles in the same structured classifier and it identifies the communication between those roles.
As the following figure illustrates, you can add a connector between two or more parts in a structured classifier.
In the above example, the class Car contains two internal composite parts: rear:Wheel[2], which represents the two rear wheels of a car, and e:Engine, which represents the engine of the car. The rearaxle connector links the engine of the car to the instances in the set rear:Wheel.
As the following figure illustrates, you can add a connector from a part to a port to link instances of one class to instances of a different class.
In the above example, the class named Boat contains a part named :Propeller, which is connected by the shaft connector to the port of e:Engine. Although the part e:Engine has the same type name in both the Car and Boat classes, the parts are different instances and each belong to a different containing classifier.
You can use both types of connectors in one containing classifier to describe the various communication links between the parts.
As the following figure illustrates, you can connect two internal parts that represent the front and rear wheels with an assembly connector, and you can also connect the internal part front:Wheel[2] to the external port of :Engine with a delegate connector.