Addresses the issue of the formal definition of hierarchical visual languages. It is motivated by interest in formal system development and the use of visual languages as formal specification tools. The paper presents a formal model of hierarchical visual languages. This model, called HIRG (hierarchical icon-replacement grammar), is then extended to enable the integration of textual and visual notations. >
['Sherif El-Kassas']
HIRG: a model for defining hierarchical visual languages