Object classes - grouping objects

Objects with common properties are often "collected" in object classes, which represent general object collections. Classes are associated with names (terms, designations) that relate to the class concept (intension) on the one hand and to the class extension on the other hand.

Often, classes are based on intentional definitions by describing, what type of objects a class consists of, i.e. by defining an object type. But there exist also extensional class definitions (especially for conceptual objects), where the elements of a class are listed explicitly. Hence, class definitions include two aspects

• Extensional definition - describes the class by referring to objects belonging to the class

• Intentional definition - provides a conceptual definition of the object type in terms of typical characteristics of the objects belonging to a class.

Classes are not given by nature, but are an expression of human knowledge and the specific view to a certain subject area. Thus, an object may belong to any number of classes, which just express different views to the objects. Usually, classes are referred to as nouns that are used as terms designated to particular class concepts.

TM will not consider classes as such, but rather these two class aspects represented by object types (intensional) and object collections (extensional).