Skip to main content

Keyword (UML)

A Keyword in UML is a predefined and reserved word available with the meta-model of UML.

Notation​

Some keywords are wrapped in an opening and a closing guillemet (U+00AB LEFT-POINTING DOUBLE ANGLE QUOTATION MARK, “«”, U+00BB RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK, “»”). A guillemet is often confused with a duplicate U+003C LESS-THAN SIGN, “<” (<<) and U+003E GREATER-THAN SIGN, “>” (>>)

wrong: <<create>>

correct: «create»

Keyword vs. Stereotype​

While the notation for some Keywords is the same as for Stereotypes, they do not necessarily refer to the same:

"[...] many use the term stereotype to mean the same as keyword, although that is no longer correct." [📖UML, 66]

Martin Fowler refers in this quote to the differences between UML 1 and UML 2, whereas in UML 1 the "guillemets where used mainly for stereotypes." [📖UML, 66]: While a Keyword is pre-defined in the meta-model of UML, a Stereotype can be a custom defined model extending an element from the UML meta-model. Stereotypes can be used for providing additional or specifying functional and semantic context in an otherwise ambiguous situation.

Example​

Keywords such as «create», «use» or «call» are used to further specify a Dependency between two elements and provide the context of the Relationship Type of this Dependency.

In the following example, a Dependency between Client and Supplier exists. Specifying the Relationship can dramatically change the understanding of the diagram.

Figure 1 The context of the dependency is not further specified.
Figure 2 The context of the dependency is specified with the keyword «create», the relationship is of type "Usage"
Figure 3 Client is now substitutable for Supplier. The relationship is now of type "Substitution"

see also

References

  1. [UML]: Fowler, Martin: UML Distilled (2004), Addison-Wesley [BibTeX]