As distribution becomes commonplace, there is a growing requirement for applications that behave reliably when node or network failures occur. To support reliability, operations on the components of a distributed application may be declared to occur within the scope of an atomic action. This thesis describes how atomic actions may be supported in an environment consisting of applications that operate on objects. To support the failure atomicity and permanence of effect properties of an atomic action, the objects accessed within the scope of an atomic action must be recoverable and persistent. This thesis describes how these properties may be added to the class of an object. The approach adopted is to provide a class that implements recovery and persistence mechanisms, and derive new classes from this base class. By refining inherited operations so that recovery and persistence is specific to that class, recoverable and persistent objects may be easily produced. This thesis also describes how an atomic action may be implemented as a class, so that instances of the class are atomic actions which manage the recoverable and persistent objects. Multiple instance declarations produce nested atomic actions, and the atomic action class also inherits persistence so that shortterm commit information may be saved in an object store which is used to maintain the passive state of persistent objects. Since the mechanisms and classes that support recovery, persistence, and atomic actions are constructed using the feature of an object-oriented language, they may be implemented in environments that provide suitable support for objects and object-oriented programming languages.

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.

The first part of the thesis provides an introduction to the logic programming language Prolog and some areas of current research. The use of compilation to make Prolog faster and more efficient is studied and a modified representation for complex structures is presented. Two programming tools are also presented. The second part of the thesis focuses on one problem which arises when implementing an Expert System using Prolog. A practical three-valued Prolog implementation is described. An interpreter accepts three-valued formulae and converts these into a Prolog representation. Formulae are in clausal form which allows disjunctive conclusions to rules. True and false formulae are stated explicitly and therefore the interpreter is able to perform useful consistency checks when information is added to the data base.

It has long been recognised that everyday dictionaries are a potential source of lexical and world knowledge of the type required by many Natural Language Processing (NLP) systems. This research presents a semi-automated approach to the extraction of rich semantic relationships from dictionary definitions. The definitions are taken from the recently published "Cambridge International Dictionary of English" (CIDE). The thesis illustrates how many of the innovative features of CIDE can be exploited during the knowledge acquisition process. The approach introduced in this thesis uses the LOLITA NLP system to extract and represent semantic relationships, along with a human operator to resolve the different forms of ambiguity which exist within dictionary definitions. Such a strategy combines the strengths of both participants in the acquisition process: automated procedures provide consistency in the construction of complex and inter-related semantic relationships, while the human participant can use his or her knowledge to determine the correct interpretation of a definition. This semi-automated strategy eliminates the weakness of many existing approaches because it guarantees feasibility and correctness: feasibility is ensured by exploiting LOLITA's existing NLP capabilities so that humans with minimal linguistic training can resolve the ambiguities within dictionary definitions; and correctness is ensured because incorrectly interpreted definitions can be manually eliminated. The feasibility and correctness of the solution is supported by the results of an evaluation which is presented in detail in the thesis.

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