The whole-part relationship in object modelling: a definition in cOlOr

In object models built according to popular object-oriented formalisms, the commonest relationship types (excluding inheritance) are the structural re lationships of association and of whole-part (often called aggregation). Th is last type is well known to have no accurately prescribed semantics. Here , some of the aggregation semantics frequently presented in the literature and sometimes supported in current object-oriented modelling languages, esp ecially UML, are analysed and criticised. Because of defects, the use of a modelling notation based on these aggregation semantics is dubious and limi ted. Moreover, many properties are candidates for characterising the whole- part relationship provided that no redundancy and no inconsistency exist be tween them. A framework known as cO1Or is then offend by means of a metamod el in which the Whole-Part metatype inherits from the Structural-Relationsh ip metatype. Defining a specific aggregation semantics leads then, first, w ithin cO1Or, to the creation of a subtype of the Whole-Part metatype. Next, the behaviour of this last type is extended and/or restricted in using a c onstraint-based approach. Such a process is developed particularly for cons idering Composition in UML and Aggregation in OML more formally, as well as for dealing with domain-dependent aggregation semantics. Since a non-negli gible feature of cO1Or is the availability of a C++ library that implements the proposed metamodel, some implementation concerns are also briefly disc ussed. (C) 2001 Elsevier Science B.V. All rights reserved.