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This chapter is from the book 16.7 Keywords

16.7 Keywords

A UML keyword is a textual adornment to categorize a model element. For example, the keyword to categorize that a classifier box is an interface is (shocking surprise!) «interface». Figure 16.1 illustrates the «interface» keyword. The «actor» keyword was used to replace the human stick-figure actor icon with a class box to model computer-system or robotic actors.

Guideline: When sketching UML—when we want speed, ease, and creative flow—modelers often simplify keywords to something like ‘<interface>’ or ‘<I>’.

Most keywords are shown in guillemet (« »)[2] but some are shown in curly braces, such as {abstract}, which is a constraint containing the abstract keyword. In general, when a UML element says it can have a “property string”—such as a UML operation and UML association end have—some of the property string terms will be keywords (and some may be user defined terms) used in the curly brace format.

Figure 16.1 illustrates both the «interface» and {abstract} keywords.

A few sample predefined UML keywords include:[3]



Example Usage


classifier is an actor

in class diagram, above classifier name


classifier is an interface

in class diagram, above classifier name


abstract element; can’t be instantiated

in class diagrams, after classifier name or operation name


a set of objects have some imposed order

in class diagrams, at an association end

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