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In 1963 Sutherland introduced the Sketchpad system, a constraint language for graphical interaction. Other early constraint programming languages were Fikes' Ref-Arf, Lauriere's Alice, Sussmann's CONSTRAINTS and Borning's ThingLab. These languages already offered the most important features of constraint programming: declarative problem modelling and efficient constraint enforcement; propagation of the effects of decisions; flexible and intelligent search for feasible solutions. Each of these three features has been the study of extensive research over a long period.

The current flowering of constraint programming owes itself to a generation of languages in which declarative modelling, constraint propagation and explicit search control are supported in a coherent architecture that makes them easy to understand, combine and apply.

Mark Wallace
Wed Sep 3 18:36:40 BST 1997