A model for object representation and manipulation in a visual design language

Languages used for design activities in CAD software are usually textual languages akin to standard procedural programming languages such as Basic or C++. This creates a discontinuity between the drafting and solid modelling aspects of design, and the programming aspects which are becoming increasingly important as designers attempt to economise on their activities by building parameterised specifications. The declarative language LSD addresses this issue by applying visual programming to design. Here we present a formal model for objects in a design space and for operations on design objects. We also show how this model is integrated with LSD to provide a general mechanism for extending the language through the addition of new operations.