Object types - what objects are

Intentional class definitions may be defined as objects types. Typing reflects a knowledge aspect based on class definitions. In order to describe details of an individual object, language refers to object properties ( first name is Paul , second name is Miller , weight is 75 kilograms or he has got children Jane , Anton and Marry ). In order to refer to object instance data, property names and its meaning have to be defined ( first name , second name , weight or children ). Thus, an object type is typically defined by a number of property definitions.

Object types are concepts that are defined by a number of fixed and variable characteristics, which describe relevant properties for objects of a given class and concept relations that describe type of relations to other objects. Characteristics and concept relations defined for an object type are called properties . Thus, object types reflect a specific perspective to a set of objects associated with this type and provide an intentional definition for objects in the object class associated with the object type.

Object properties may be divided into four categories:

• Generalization - describes a concept that relates to a more general object type.

• Characteristic - describes a fixed or variable characteristic of an object

• Part (of) - describes the parts an object consists of

• Association - describes the relations to other objects

Those property categories are defined in concept systems as concept relations and characteristics [1087]. In data modeling they are known as inheritance, attributes and relationships [ODMG]. [UML] refers to property categories as generalization, attributes, aggregation and association. More relations are known between concepts as near or related concepts, i.e. this list of property categories is not complete. But the categories mentioned above are those that are considered as most relevant property categories for defining a terminology model as bridge between subject area and IT experts.

There is not always a clear distinction between property categories defined for an object type. E.g. whether a wheel is a part of a car or whether it is associated with a car depends on the view one has to the car. Thus, an object type does not define an object as such, but a certain view to objects of a given class. Moreover, properties do not describe all the properties of an object, but properties relevant from a certain perspective, only - the expert's view.

Many properties refer to other objects, which, again, are associated with an object type that defines properties etc. Thus, there is an alternative type - property - type - property ... relation, which provides a method of defining a terminology model in a consistent way until any level of detail. The alternating sequence usually ends, when a property refers to a type that does not have properties (elementary type or classification).