GVL: Visual specification of graphical output

The conceptual view model of output is based on the complete separation of the output specification of a program from the program itself, and the use of implicit synchronization to allow the data state of the program to be continuously mapped to a display view. An output specification language called GVL is used to specify the mapping from the program’s data state to the display. GVL is a functional language explicitly designed for specifying output. Building from a small number of basic primitives, it provides sufficient power to describe complex graphical output. Examples shown in the paper include GVL specifications for linked list diagrams, bar charts and an address card file. In keeping with its intended application, GVL is also a visual language in which the user draws output specifications directly on the display. It is shown how problems often associated with imperative graphical languages are avoided by using the functional paradigm. A prototype implementation of GVL was used to produce all examples of graphical output in the paper.