Graceful interaction with graphical constraints

The graphical constraint editor (GRACE), a graphical editor that lets users define graphical, or geometric, constraints, is reviewed. Graphical constraints specify relationships among graphical objects that the system must maintain. Constraints are useful in graphical drawing editors, design activities supported by CAD systems, and graphical user interface construction. GRACE provides mechanisms for explicit and implicit constraint specification using simple and natural means. These include simple direct manipulation methods and a constraints-by-demonstration facility that incorporates both novel heuristics for inferring user-demonstrated relations in an economical fashion and a natural-language explanation tool that helps the user understand the system´s inferencing behavior. An overview of GRACE´s user interface is presented and details about how users specify graphical relations and query the system to obtain information about them are provided.<>