Parts

A part is a property that defines a partitive or owning relation to one or more object instances of a given object type. In [1087] parts are referenced as partitive concept relations. The object model [ODMG] considers part-of relations as relationships or complex attributes.[UML] supports partitive relations as composite aggregations. [ERM] defines partitive relations as table relations but not as instance relations.

Technically, it is not possible to draw a clear borderline between partitive and associative concept relations or characteristics. Conceptually, it makes a big difference, whether parts of an object instance are considered to be dependent on or owned by the referencing instance or not. It depends, however, on the specific view, whether one considers e.g. wheels as part of a car or as association between car and wheels.

Technically, part properties might be implemented as parts, complex attributes or as relationships, depending on the features supported by the target system.