Multi-way versus One-way Constraints in User Interfaces: Experience with the DeltaBlue Algorithm

The e cient satisfaction of constraints is essential to the performance of constraint-based user interfaces. In the past, most constraint-based user interfaces have used one-way rather than multiway constraints because of a widespread belief that one-way constraints were more e cient. In this paper we argue that many user interface construction problems are handled more naturally and elegantly by multi-way constraints than by one-way constraints. We present pseudocode for an incremental multi-way constraint satisfaction algorithm, DeltaBlue, and describe experience in using the algorithm in two user interface toolkits. Finally, we provide performance gures demonstrating that multi-way constraint solvers can be entirely competitive in performance with one-way constraint solvers. This is a preprint of a paper that will appear in the journal Software|Practice and Experience in 1993. It is a slightly revised version of Technical Report 92-07-05, July 1992.