An Object - Oriented Approachto Formal

Formal methods for software development are becoming increasingly necessary as softwarebecomes an important part of everyday life. To handle the complexities inherent in large-scale software systems these methods need to be combined with a sound developmentmethodology which supports modularity and reusability. Object orientation, based on theconcept that systems are composed of collections of interacting objects whose behavioursare speci ed by classes, is such a methodology.This thesis presents the formal speci cation language Object-Z which is an extension ofthe formal speci cation language Z to facilitate speci cation in an object-oriented style.The major extension in Object-Z is the introduction of the class schema which capturesthe object-oriented notion of a class by encapsulating a single state schema with all theoperation schemas which may a ect its variables. The class schema is not simply asyntactic extension but also de nes a type whose instances are objects. Object-Z alsosupports single and multiple inheritance allowing classes to be reused in the de nitionof other classes and polymorphism allowing a variable to be assigned to objects of morethan one class.The thesis also presents a set-theoretic model of classes in Object-Z which could form thebasis of a full formal semantics. The model, based on the histories of a class, i.e. thesequences of states and operations which an object of the class can undergo, facilitatesthe speci cation of liveness properties using a temporal logic notation. A fully-abstractmodel of classes in Object-Z, derived from the history model, is also presented. Thismodel is used to formally de ne a notion of behavioural compatibility in Object-Z whichcould form the basis of a theory of class re nement. AcknowledgementsI would like to express my sincere thanks to my supervisor, Dr Roger Duke, for hiscomments and guidance as the ideas in this thesis evolved, and for his unremitting en-couragement and help when they weren't evolving so well. I would also like to thank thefollowing people without whose contributions to the development of Object-Z, this thesiswould not have been possible { Gordon Rose, Paul King, David Duke and David Car-rington. Thanks go also to Ian Hayes, Cecily Bailes and Anthony Lee for their invaluablecomments and suggestions.I would like to acknowledge the generous nancial support provided by the OverseasTelecommunications Corporation (OTC) of Australia and the Commonwealth Govern-ment of Australia in the form of postgraduate awards. I would also like to acknowledgethe Department of Computer Science for support in the form of a research scholarshipand tutorship, and for nancing attendance at several conferences both in Australia andoverseas.Finally, I would like to acknowledge the support of my family and friends. To my parents,I express my love and gratitude for their encouragement and nancial support in myearlier years of study. I also, especially, thank Kim for her continuing love, patience andunderstanding.