An expression model for graphical command languages

A unified command model for interactive systems is presented based on the expression syntax of PASCAL-like languages. The relationships between command specification and feedback as they relate to command structure are reviewed for both continuous and discrete interactions. The advantages of a discrete prefix command structure are presented in relationship to the PASCAL expression mechanism.The procedure mechanism of PASCAL-like languages is presented as a basis for graphical command specifications. The advantages of such a model are discussed in terms of borrowed knowledge from compiler construction and user familiarity. The automatic generation of interactive systems from such a model is discussed.An extended example of how procedure declarations can serve as the basis for interactive command definition is given. It is shown how menu-driven systems can be automatically generated from such a description. It is also shown how by extending the procedure declaration it is possible to support iconic identifiers, function buttons and locater and valuator type devices.The role of data types in such a command model is explored in depth. The notion of using a typed data value as a pick identifier is presented. It is shown how such typed identifiers can be integrated into the command model to provide automatic error checking and resolution of ambiguous pointing.