The article addresses the formal specification, design and implementation of the behavioral component of graphical user interfaces. The complex sequences of visual events and actions that constitute dialogs are specified by means of modular, communicating grammars called VEG (Visual Event Grammars), which extend traditional BNF grammars to make them more convenient to model dialogs.A VEG specification is independent of the actual layout of the GUI, but it can easily be integrated with various layout design toolkits. Moreover, a VEG specification may be verified with the model checker SPIN, in order to test consistency and correctness, to detect deadlocks and unreachable states, and also to generate test cases for validation purposes.Efficient code is automatically generated by the VEG toolkit, based on compiler technology. Realistic applications have been specified, verified and implemented, like a Notepad-style editor, a graph construction library and a large real application to medical software. It is also argued that VEG can be used to specify and test voice interfaces and multimodal dialogs. The major contribution of our work is blending together a set of features coming from GUI design, compilers, software engineering and formal verification. Even though we do not claim novelty in each of the techniques adopted for VEG, they have been united into a toolkit supporting all GUI design phases, that is, specification, design, verification and validation, linking to applications and coding.

The paper addresses the formal specification, design and implementation of the behavioral component of graphical user interfaces. Dialogs are specified by means of modular, communicating grammars called VEG (Visual Event Grammars), which extend traditional BNF grammars to make the modeling of dialogs more convenient. A VEG specification is independent of the actual layout of the GUI, but it can be easily integrated with various layout design toolkits. The specification may be verified with the model checker Spin, in order to test consistency and correctness, to detect deadlocks and unreachable states, and also to generate test cases for validation purposes. Efficient code is automatically generated by the VEG toolkit, based on compiler technology. Realistic applications have been specified, verified and implemented, like a Notepad-style editor, a graph construction library and a large real application to medical software. The complete VEG toolkit is going to be available soon as free software.

The purpose of the paper is to present the implications of a new definition of context-free languages. The main interests of this approach are first to allow full formal proofs and second to enlight the crucial role of rational closures. The proposed formalism is based on a theorem of Wechler. It is very near to the “radical algebras” of Conway.