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Most computing systems are shared between users of various kinds. This thesis treats such systems as mathematical objects, and investigates two of their properties: refinement and security. The first is the analysis of the conditions under which one shared system can be replaced by another, the second the determination of a measure of the information flow through a shared system. Under the heading of refinement we show what it means for one shared system to be a suitable replacement for another, both in an environment of co-operating users and in an environment of independent users. Both refine- ment relations are investigated, and a large example is given to demonstrate the relation for cooperating users. We show how to represent the security of a shared system as an 'inference function', and define several security properties in terms of such functions. A partial order is defined on systems, with the meaning 'at least as secure as'. We generalise inference functions to produce 'security specifications' which can be used to capture the desired degree of security in any shared system. We define what it means for a shared system to meet a security specification and indicate how implementations may be derived from their specifications in some cases. A summary of related work is given.

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With ever cheaper and more powerful technology. the proliferation of computer systems, and higher expectations of their users, the user interface is now seen as a crucial part of any interactive system. As the designers and users of interactive software have found, though, it can be both difficult and costly to create good interactive software. It is therefore appropriate to look at ways of "engineering" the interface as well as the application. which we choose to do by using the software engineering techniques of specification and prototyping. Formally specifying the user interface allows the designer to reason about its properties in the light of the many guidelines on the subject. Early availability of prototypes of the user interface allows the designer to experiment with alternative options and to elicit feedback from potential users. This thesis presents tools and techniques (collectively called SPI) for specifying and prototyping the dialogues between an interactive system and its users. They are based on a formal specification and rapid prototyping method and notation called me too. and were originally designed as an extension to me too. They have also been implemented under UNIX*. thus enabling a transition from the formal specification to its implementation. *UNIX is a trademark of AT&T Bell Laboratories.

Thesis (M.S.)--Rutgers University, 2007. / "Graduate Program in Electrical and Computer Engineering." Includes bibliographical references (p. 68-71).