The SkyBlue Constraint Solver and Its Applications.
Michael Sannella · 1993
The SkyBlue constraint solver is an efficient incremental algorithm that uses local propagation to maintain sets of required and preferential constraints. SkyBlue is a successor to the DeltaBlue algorithm, which was used as the constraint solver in the ThingLab II user interface development environment. Like DeltaBlue, SkyBlue represents constraints between variables by sets of short procedures (methods) and incrementally resatisfies the set of constraints as individual constraints are added and removed. DeltaBlue has two significant limitations: cycles of constraints are prohibited, and constraint methods can only have a single output variable. SkyBlue relaxes these restrictions, allowing cycles of constraints to be constructed (although SkyBlue may not be able to satisfy all of the constraints in a cycle) and supporting multi-output methods. This paper presents the SkyBlue algorithm and discusses several applications that have been built using SkyBlue. 1 Introduction The DeltaBlue a...