An Interface realization is a specialized Realization relationship between a Classifier Behavior and an Interface, signifying that the realizing classifier conforms to the contract specified by the Interface.

A classifier that implements an interface specifies instances conforming to the interface and its ancestors. A classifier may implement a number of interfaces.

In the Interface realization Specification window, you can modify the current element and add various specifications to it. 
 
To open the Interface Realization dialog box, choose the Specification command from the Realization shortcut menu.
 

In the Interface Realization Specification window, the Implementing Classifier property references the classifier that realizes the Interface to which it points.