Logic-based visual languages for manipulating structures

In many interactions with computers, users accomplish tasks by manipulating visual representations of objects. Having noted that logic programming provides a simple but powerful mechanism for manipulating complex symbolic structures (unification), we are investigating ways to apply variants of this mechanism to structures with concrete visual representations. Accordingly, we are applying logic programming in two domains where manipulation of visual structures is of key importance: designing complex parametrised structured objects, and spreadsheet programming and design. We have proposed a logic-based visual language for structured design (LSD), which integrates concrete representations of design components with operations that specify how components are assembled, and have shown how the definition of "design space", on which LSD depends, naturally captures the notion of the behaviour of complex components; how design synthesis and assembly of structured objects can be integrated; and how domain-specific operations on components might be animated. Our long term goal is to develop a formal basis for visual design languages, sufficiently general to apply to a wide range of industrial design domains. This has the potential to make an important contribution to industrial design. Spreadsheets, in their current form, have limited programming facilities, minimal abstraction facilities, and no sound software engineering tools or methodology. As a result, despite the fact that they are used for critical applications, they are among the most error-prone of programming tools. We have shown that by defining a form of unification that applies to arrays, logic programming can be added to spreadsheets to provide facilities for programming abstractions in the sheet interface, and specifying spreadsheet structure. Our goal is a spreadsheet model which supports the "formula-in-cell" programming familiar to spreadsheet users, while providing tools to help users build robust and reliable spreadsheet applications.