Direct manipulation user interfaces based on constraints

Object-oriented user interface technology increases the productivity of interface designers and programmers. However, there are some shortcomings to the object-oriented approach. An approach that is based on the concept of separating the presentation from the application data is presented. While in object-oriented user interfaces presentation and application data communicate via a protocol of procedure cells, in this approach the relationships are described declaratively with structured sets of maintained constraints. An overall architecture based on constraints that encompasses all aspects of a user interface is described. The procedural behavior of a user interface is achieved through constraint satisfaction