A user-centred approach to functions in Excel

Abstract

We describe extensions to the Excel spreadsheet that integrate user-defined functions into the spreadsheet grid, rather than treating them as a "bolt-on". Our first objective was to bring the benefits of additional programming language features to a system that is often not recognised as a programming language. Second, in a project involving the evolution of a well-established language, compatibility with previous versions is a major issue, and maintaining this compatibility was our second objective. Third and most important, the commercial success of spreadsheets is largely due to the fact that many people find them more usable than programming languages for programming-like tasks. Thus, our third objective (with resulting constraints) was to maintain this usability advantage.Simply making Excel more like a conventional programming language would not meet these objectives and constraints. We have therefore taken an approach to our design work that emphasises the cognitive requirements of the user as a primary design criterion. The analytic approach that we demonstrate in this project is based on recent developments in the study of programming usability, including the Cognitive Dimensions of Notations and the Attention Investment model of abstraction use. We believe that this approach is also applicable to the design and extension of other programming languages and environments.