Parts are run-time instances of Classes or Interfaces. Multiplicity can be specified for a Part, using the notation:
where x specifies the initial or set number of instances when the composite structure is created, and y indicates the maximum number of instances at any time.
Parts are used to express composite structures, or modeling Patterns that can be invoked by various objects to accomplish a specific purpose. When illustrating the composition of structures, Parts can be embedded as properties of other Parts. When embedded as properties, Parts can be bordered by a solid outline, indicating the surrounding Part owns the Part by composition. Alternatively, a dashed outline indicates that the property is referenced and used by the surrounding Part, but is not composed within it.