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Object-oriented programming languages provide a powerful interface for programmers to access the mechanisms necessary for reliable distributed computing. Using inheritance and polymorphism provided by the object model, it is possible to develop a hierarchy of classes to capture the semantics and inter-relationships of various levels of functionality required for distributed transaction processing. Using multiple inheritance, application developers can selectively apply transaction properties to suit the requirements of the application objects. In addition to the specific problems of (distributed) transaction processing in an environment of persistent objects, there is a need for a unified framework, or architecture in which to place this system. To be truly effective, not only the transaction manager, but the entire transaction support environment must be described, designed and implemented in terms of objects. This thesis presents an architecture for reliable distributed processing in which the management of persistence, provision of transaction properties (e.g., concurrency control), and organisation of support services (e.g., RPC) are all gathered into a unified design based on the object model.

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Formal methods are increasingly accepted for developing software systems, however their application to user-interface development is less common. In this thesis, we demonstrate the utility of formal object-oriented techniques for specifying, designing and implementing user-interfaces. The specification of a user-interface describes user-perceivable operations and information structures for an interactive system in an implementation-independent way. Operations of a user-interface specification define tasks. User-interfaces can be specified by a system of communicating agents where some agents are presented to users. An agent and its presentation together define an interactor. Defining the presentation of interactors is a design concern. Widgets are common re-usable interactors for which the presentation is usually well defined. Definitions of widgets may be stored in a library. We illustrate the characteristics of notations for interactor based specification using the Object-Z language and demonstrate using interactors from a widget library. Formal methods enable a "model-based" approach to be taken to the development of user-interface designs. A specification in terms of widgets is derivable from an abstract interactor-based specification. A corresponding user-interface design is usually easily identified from a widget-based specification. Interactor-based user-interface designs can be used to define an architecture for a corresponding system implementation. Derivation of a widget-based specification from an abstract specification corresponds to a task decomposition (i.e., the abstract and widget-based specifications enable the same tasks to be performed, although the operations involved differ). Task decomposition defines a compatibility relation between user-interface specifications. We give "specification patterns" to assist incrementally transforming an abstract user-interface specification to an equivalent specification in terms of widgets.