Behavioural Mapping for Service Substitutability

Service substitutability is now a challenge in the area of objectoriented systems. This is due to the restriction of the underlying type systems that recognise only syntactic compatibility which is based on the supported subtyping rules. This paper presents an idea to add behavioural mapping for flexible substitutability of services to a distributed object system. The complete implementation applies the idea to provide substitutability between versions of a service in which evolution of the service results in arbitrary change in the service interface, i.e. change which is not necessarily limited to the form of subtypes. The mechanism is done by a mediator object which is capable of transforming the behaviour of the service into the form expected by its clients by using some user-defined mapping functions. Such behavioural mapping can also be used to improve service selection.