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A classifier is a category of Unified Modeling Language (UML) elements that have some common features, such as attributes or methods.
A classifier is an abstract metaclass classification concept that serves as a mechanism to show interfaces, classes, datatypes and components.
A classifier describes a set of instances that have common behavioral and structural features (operations and attributes, respectively).
A classifier is a namespace whose members can specify a generalization hierarchy by referencing its general classifiers.
A classifier is a type and can own generalizations, thereby making it possible to define generalization relationships to other classifiers.
A classifier is a redefinable element, as it is possible to redefine nested classifiers.
All objects that can have instances are classifiers.
Types of UML Classifiers
Predefined UML classifiers