Scattered Associations in ObjectOriented Modelling.pdf

Scattered Associations in Object-Oriented Modelling Kasper Østerbye Norwegian Computing Center, Postboks 114 Blindern, 0314 OSLO, Norway. Kasper.Osterbye@nr.no Johnny Olsson WM-data, Hermodsvej 22, 8230 Åbyhøj, Århus, Denmark, jooln@ Abstract. The popularity of UML has bought a new abstraction mechanism, as- sociations, into the realm of object-oriented programming. Associations are used in the analysis and design phases of software development. We have used UML in a paper and pencil redesign of a large existing system where the goal was to move from a relational model to an object-oriented model. Our experi- ence has shown us that the concept of associations in UML is very useful, but also that there are several shortcomings regarding their expressive power. Scat- tered associations are global association structures whose definition is scattered throughout a UML diagram. We have identified two kinds of scattered associa- tions. A structural association is a scattered association that defines the struc- ture of a set of objects, and a co-variant association is a scattered association that describes pair-wise parallel inheritance hierarchies. 1 Introduction The graphical modelling language UML [Rational, 1998] has brought associations into object-oriented modelling, and seem to complement the existing modelling capa- bilities well. A hallmark of object-oriented modelling has been its closeness to human conceptualisation, with objects representing nouns, and methods/functions/procedures representing verbs. Associations can be said to model the word class, transitive verbs, with one object being the subject