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18.16.  Interface

An interface is a set of operations characterizing the behavior of an element. It can be usefully thought of as an abstract class with no attributes and no non-abstract operations. In the UML metamodel it is a sub-class of Classifier and through that GeneralizableElement.

An interface is represented on a class diagram as a rectangle with two horizontal compartments. The top compartment displays the interface name (and above it «interface») and the second any operations. Just like a class, the operations compartment can be hidden.

18.16.1.  Interface Details Tabs

The details tabs that are active for interfaces are as follows.


Standard tab.


See Section 18.16.2, “ Interface Property Toolbar and Section 18.16.3, “ Property Fields For Interface below.


Standard tab. See Section 13.4, “ Documentation Tab.


Standard tab. The tick box Display Operations allows the operation compartment to be shown (the default) or hidden. This is a setting valid for only the current diagram. The Bounds: field defines the bounding box for the package on the diagram.


Standard tab. This contains a template for the interface declaration and declarations of associated interfaces.

Tagged Values

Standard tab. In the UML metamodel, Interface has the following standard tagged values defined.

  • persistence (from the superclass, Classifier). Values transitory, indicating state is destroyed when an instance is destroyed or persistent, marking state is preserved when an instance is destroyed.


    Since interfaces are by definition abstract, they can have no instance, and so this tagged value must refer to the properties of the realizing class.

  • semantics (from the superclass, Classifier). The value is a specification of the semantics of the interface.

  • derived (from the superclass, ModelElement). Values true, meaning the interface is redundant -it can be formally derived from other elements, or false meaning it cannot.


    Derived interfaces still have their value in analysis to introduce useful names or concepts, and in design to avoid re-computation.


The UML Element metaclass from which all other model elements are derived includes the tagged element documentation which is handled by the documentation tab under ArgoUML


Standard tab for an Interface.

18.16.2.  Interface Property Toolbar

Go up

Navigate up through the package structure.

New operation

This creates a new operation (see Section 18.8, “ Operation) within the interface, navigating immediately to the properties tab for that operation.

New reception

This creates a new reception, navigating immediately to the properties tab for that reception.

New interface

This creates a new interface in the same namespace as the selected interface, navigating immediately to the properties tab for the new interface.

New Stereotype

This creates a new Stereotype (see Section 16.6, “ Stereotype) for the selected interface, navigating immediately to the properties tab for that stereotype.


This deletes the interface from the model


This is a deletion from the model not just the diagram. To delete an interface from the diagram, but keep it within the model, use the main menu Remove From Diagram (or press the Delete key).

18.16.3.  Property Fields For Interface


Text box. The name of the interface. The name of an interface has a leading capital letter, with words separated by “bumpy caps”.


Unlike classes, the ArgoUML critics will not complain about interface names that do not have an initial capital.


Drop down selector. Interface is provided by default with the UML standard stereotypes for the parent meta-class, Classifier ( metaclass, powertype, process, thread and utility).

Navigate Stereotype

icon. If a stereotype has been selected, this will navigate to the stereotype property panel (see Section 16.6, “ Stereotype).


Drop down selector. Records and allows changing the namespace for the interface. This is the package hierarchy.


Check box, with entries Abstract, Leaf and Root.

  • Abstract is used to declare that this interface cannot be instantiated, but must always be specialized. The name of an abstract interface is displayed in italics on the diagram.


    This is meaningless, since by definition an interface is an abstract entity. The UML 1.3 standard offers no clarification.

  • Leaf indicates that this interface cannot be further specialized, while Root indicates it can have no generalizations.


Radio box, with three entries public, protected, private and package. Indicates whether navigation to this end may be by: i) any classifier; ii) only the source classifier and its children; or iii) only by the source classifier.


Text area. Lists any interface that generalizes this interface.

Button 1 double click navigates to the generalization and opens its property tab.


Text box. Lists any specialized interface (i.e. for which this interface is a generalization.

Button 1 double click navigates to the generalization and opens its property tab.


Text box. Lists any AssociationEnds (see Section 18.13, “ Association End) connected to this interface.


Associations between classes and interfaces must be navigable only from the class to the interface. ArgoUML will create associations between classes and interfaces with the correct navigability, but does not prevent the user from altering this.

Button 1 double click navigates to the selected entry.


Text area. Lists all the operations (see Section 18.8, “ Operation) defined on this interface. Button 1 double click navigates to the selected operation. Button 2 click will show a popup menu with two items: Move Up and Move Down, which allow reordering the operations.


All operations on an interface must be public. The ArgoUML critics will complain if this is not the case.