Abstract
Formal methods have been used to develop a prototype interactive editing system, in which different edits are viewed through separate windows. Designing the prototype has involved the development of a simple window management system. The design of the window manager was achieved with the assistance of an initial description using an abstract model of interaction. We argue that abstract interaction models clarify certain design issues. We discuss more complex properties of windowing systems including separability, sharing and interference. We formulate some simple generative user-engineering principles to support these properties.

Abstract
User-centered design imposes constraints on the programmer-centered approach to program development. In this paper we describe a practical experiment using a three level design approach which incorporates at its top level an abstract model of interaction. The interaction model is used as the basis for proof that user-centred design principles hold for the system design. We also discuss refinement methods which achieve certain structural optimisations through the technique of 'interface drift'. A real system has been produced by these methods and is being used as a basis for test of alternative empirical evaluation techniques.

Abstract
This paper is a brief report on the initial phase of the formal development of a graphics programming system. At this stage of the specification, the system architecture is just outlined and attention is focussed on the conceptual level. The abstract notion of a graphic 'archetype' is introduced and proposed as a basis for the style of graphics programming to be implemented. The formal description of this meta-concept of the system is sketched.

Abstract
The basic function of an electric power system is to satisfy the customer energy requirements as economically as possible and at an adequate level of continuity and quality. Reliability calculations such as those described in this paper can be used with advantage in establishing additional security constraints, that if used in the right context and backed up by the inevitable economic analysis, provide better and more consistent information for system planning or expansion studies. The model described can also be used when the simulation of the actual operating conditions is necessary.

Abstract

Abstract
However sophisticated a development environment may be it is inevitable that some diagnosis takes place in the target system. When the target consists of a number of processors co-operating in a complex way diagnosis can be extremely difficult to achieve. This paper describes techniques for monitoring behaviour in a target system so that there is minimal disturbance. The information collected can be used subsequently to simulate the run in the host where the full set of debugging tools can be used. These techniques are being used as guidelines in a research project funded under the UK Alvey initiative. © 1985.