What is Common Between Generic Services and Interface Navigation?

Generic services and interface navigation in object oriented systems can be formulated in terms of specific typecasting sequences over narrowing and widening operations. With examples, the commonality and difference between the two are brought out with reference to typecasting. Consequences of specific typecasting sequences to their implementation in a distributed environment are highlighted. 1 A GENERIC SERVICE A generic service is applicable to various contexts, since it is designed to cover a wide range of types. A naming service such as CORBA naming service [5] is an example of a generically applicable service in a distributed environment. The service essentially maintains mappings from object names to object handles, with object name as key. To make naming service a generically applicable component, it must not be made to handle actual object types. For example, with reference to the class hierarchy shown in Figure 1, a naming service that maps object names to handles of type LocatableObject is a generic component. Whereas, a naming service designed to map object names to objects of type ObjectType2 is not a generic component. The former is applicable to hold object name, object handle tuples for any type of object in the hierarchy, whereas, the latter can only handle objects of type ObjectType2. WHAT IS COMMON BETWEEN GENERIC SERVICES AND INTERFAE NAVIGATION? 126 JOURNAL OF OBJECT TECHNOLOGY VOL. 1, NO. 1 2 INTERFACE NAVIGATION Interface navigation allows a client having a handle to an object through one of its multiple interfaces to navigate through its other interfaces. Consider the class hierarchy shown in Figure 2. By interface navigation, a client having a handle to one of all the interfaces implemented by a shared implementation may be allowed to obtain a handle to any of the N interfaces implemented by the shared implementation. ObjectType1 LocatableObject ObjectTypeAny ObjectType2 ... Figure 1. Hierarchy in a Generic Service InterfaceType1 InterfaceType2 InterfaceTypeN