Part-whole relationship categories and their application in object-oriented analysis

Part decomposition and conversely, the construction of composite objects from individual parts have long been recognized as ubiquitous and essential mechanisms involving abstraction. This applies, in particular, in areas such as CAD, manufacturing, software development and computer graphics. Although the part-of relationship is distinguished in object oriented modeling techniques, it ranks far behind the concept of generalization/specialization and a rigorous definition of its semantics is still missing. We first show in which ways a shift in emphasis on the part-of relationship leads to analysis and design models that are easier to understand and to maintain. We then investigate the properties of part-of relationships in order to define their semantics. This is achieved by means of a categorization of part-of relationships and by associating semantic constraints with individual categories. We further suggest a precise and, compared with existing techniques, less redundant specification of constraints accompanying part-of categories based on the degree of exclusiveness and dependence of parts on composite objects. Although the approach appears generally applicable, the object oriented Unified Modeling Language (UMF) is used to present our findings. Several examples demonstrate the applicability of the categories introduced