MaramaTatau: Extending a domain specific visual language meta tool with a declarative constraint mechanism

It is increasingly common to use metatools to specify and generate domain specific visual language tools. A common problem for such metatools is specification of model level behaviours, such as constraints and dependencies. These often need to be specified using conventional code in the form of event handlers or the like. We report our experience in integrating a declarative constraint/dependency specification mechanism into a domain specific visual language metatool, focussing on the tradeoffs we have made in the notational design and environmental support used. The expressive power of the mechanism developed is illustrated by a substantial case study where we have redeveloped a complex visual tool for architectural modelling, eliminating conventional event handlers.