Consistent benefits for the system designer and the end-user.
Command languages which are internally consistent are said to be easier to learn. The level of consistency - or degree of user complexity - of any command language is usually defined using one of a number of formal grammars, and yet consistency need not be so rigorously defined. It is proposed that diagrams can provide a suitable meta-language with which to illustrate the consistent properties of any command set; and a particular type of diagram - the 'command wheel' - is described. Command wheels offer a number of advantages over formal specifications, being simple to construct and allowing more discretion in the design process. In a study of word-processor users, it was found that properties of command wheels allowed the accurate prediction of user's behaviour, both in terms of their on-line performance, and their subsequent ability to recall commands.
Briggs
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Department of Psychology, City of London Polytechnic, UK.