Graphical constraints in CoDraw

Constraint based drawing programs require users to understand and manage relationships between drawing elements. By establishing constraint relationships among elements the user effectively programs the drawing´s behavior. This programming task requires a more sophisticated visual interface than conventional drawing programs provide. Users must have available-in a convenient format-information about the structure of the constraints that determine the drawing´s interactive edit behavior. This format must support editing and debugging. CoDraw is a constraint based drawing program that can be interactively extended by its users. This paper describes the CoDraw program and its programming interface