Two-dimensional visual programming and three-dimensional execution visualisation in Prolog

A new, simple, expressively complete visual formalism for programming in Prolog is presented. The formalism is shown to be equivalent to the standard textual notation for Prolog. Some aspects of Prolog programs are identified that appear to be clearer for novices when presented in the graphic formalism, while other aspects of Prolog are noted that may be clearer in the standard textual notation. The design of an implemented computer environment dubbed VPP (short for `Visual Programming in Prolog´) is presented that supports visual programming in Prolog using the graphical formalism. Two different implemented experimental prototypes of VPP are discussed. An extension of the programming environment is described that allows Prolog execution spaces to be visualised in complete detail (or presented in various compressed, pruned or abstracted forms) using a simple three-dimensional extension of the same formalism