Objects model phenomena and a phenomenon is usually a component. Information characterizing a component is encapsulated and accessible only by its methods. The relations between components are modeled explicitly by means of associations or references. A relation is also a phenomenon and objects can model this type of phenomena too. Components are usually related conceptually in diverse and subtle ways: Some relations are implicitly given and some are local to other more basic relations. Such

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... ds of relations are important for understanding the organization and cooperation of objects and may be supported in object-oriented analysis, design, and programming: An implicit association describes a relation between an object and objects local to this enclosing object, and a complex association describes an explicit relation between local objects in different enclosing objects. Such associations are described by classes and the objects have the usual properties including methods and attributes.