Object-Oriented Software Development with UML - UNU-IIST ...

Conceptual Model – Associations 61Bicycle11 20..2Frame Wheel Light1 *RimSpoke1University * 1Department * DivisionHand10..7FingerFigure 5.11: Aggregations1. Antisymmetry: this states that if an object R is related to an object l by an aggregation, then it is notpossible for l to be related to R by the same aggregation. In other words, if l is a part of R then Rcannot be a part of l .2. Transitivity: this states that if R is related to l by an aggregation link, and l is related to I by thesame aggregation, then R is also linked to I .When to show aggregationHere are some guidelines that suggest when to show aggregation:=The lifetime of the part is bound within the lifetime of the composite–there is a create-delete dependencyof the part on the whole. The part may not exist outside of the lifetime of the whole.There is an obvious whole-part physical or logical assembly.=Some properties of the composite propagate to the parts, such as its location.=Operations applied to the composite propagate to the parts, such as destruction, movement, recording.=If you are not sure when to use it, ignore it and stick to plain association. Most of the benefits of=discovering and showing aggregation relate to the software solution phases.Based on the above discussion, we can polish the conceptual model in Figure 5.10 by replacing the Containinassociation between SalesLineItem and Sale, and the Contains association between ProductCatalog andReport No. 259, July 2002UNU/IIST, P.O. Box 3058, Macau