The design of structured objects is frequently accomplished with the use of Computer-Aided Design (CAD) systems, some of which allow for parametrised designs, which represent families of objects. Some existing CAD systems permit parametrisation by providing interfaces to programming languages, leading to a sharp division between the visual and programming aspects of building complex designs. In previous work, a design language LSD was proposed, which used visual logic programming to over-come this separation and provides "assembly semantics" for building an instance of a parametrised design corresponding to specific parameter values.

Also of interest to designers, however, is the behaviour of the objects they design. For example, the point of building a mechanical device such as an internal combustion engine is to obtain a particular mechanical behaviour. Here we extend the formal model for solid objects on which LSD relies in order to support the definition of particular kinds of behaviours.