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Abstract class
An abstract class is one for which there are no instances. It serves only as a base class, containing attributes and operations that are inherited by its derived classes. In UML notation, an abstract class is denoted by the text string {abstract}, located in the top-most compartment of the class, just under the class name.
To denote a class as abstract, select Abstract in the Definition dialog box for the class.
See also
UML class diagrams