Witten, Ian HGreenberg, Saul2008-05-262008-05-261989-12-01http://hdl.handle.net/1880/46615Current user interfaces fail to support some work habits that people naturally adopt when interacting with general-purpose computer environments. In particular, users frequently and persistently repeat their activities (eg command lines, menu selections), but computers do little to help them to review and re-execute earlier ones--at most providing ad hoc "history mechanisms" founded on the premise that the last few inputs form a reasonable selection of candidates for re-use. This paper provides theoretical and empirical foundations for the design of a general facility that helps people to recall, modify and re-submit their previous activities to computers. It abstracts several striking characteristics of repetition behaviour from usage data gleaned from many users of different systems. It presents a general model of interaction called recurrent systems. Particular attention is paid to the repetition of command lines given a sequential "history list" of previous ones, and this distribution can be conditioned in several ways to enhance predictive power. Reformulated as empirically-based general principles, the model provides design guidelines for reuse facilities specifically and modern user interfaces generally. A brief case study of actual use of a widely-available history system is included.EngComputer Scienceunknown1989-375-37http://dx.doi.org/10.11575/PRISM/31195