Intensional and extensional aspect

A specific view to a group of individual objects depends on the higher context that created this view. E.g. the view to a person is different from a statistician's point of view or from the one of a tax authority. Thus, specific views to objects may be defined within a certain context or as subordinated concepts of another concept. Such a view to an object defines the intensional aspect of the related concept, the object type.

An object type is a concept that defines a specific view to a group of individual objects, i.e. it defines the intensional aspect of a general object by means of subordinated concepts with different roles.

Since there are different views possible to any group of individual objects, several object type definitions may apply to an individual object. Considering an object as an entity in the real world (even though it becomes always difficult to drawborderlines for an object), each object type definition applying to an individual object creates an image of the object called object instance. Since different views to objects are possible, individual objects may be associated with different object types. Thus, several types may apply to an individual object and any number of object instances may exist for an individual object (e.g. the person Paul Miller might be reflected as student, patient and twice as employee), i.e. there is a 1:M relationship between individual objects and object instances.