Black and white diamonds

Abstract

This study of the semantics of UML’s shared aggregation and composition (black and white diamonds) is based on previous detailed analyses of the semantics of aggregation in object modelling in which primary axioms were identified. All forms of aggregation must comply with these primary axioms. We conclude that both kinds of UML Aggregation do not possess the full complement of primary characteristics and that their secondary characteristics, which define various “flavours” of aggregation, are overlapping and incomplete. We recommend revisions to UML’s two kinds of aggregation: completion of the primary set of axiomatic characteristics and then careful selection of secondary characteristics for defining black and white diamond aggregation.