A Visual Syntax for Logic and Logic Programming

It is commonly accepted that non-logicians have difficulty in expressing themselves in first-order logic. Part of the visual language community is concerned with providing visual notations which use visual cues (‘declarative diagrams’) to make the structuring of logical expressions more intuitive. One of the more successful metaphors used in such diagrammatic languages is that of set inclusion, making use of the graphical intuitions which most of us are taught at school. Existing declarative diagrammatic languages do not make full use of such set-based intuitions. We present a more uniform use of sets which allow simple but highly expressive diagrams to be constructed from a small number of primitive components. These diagrams provide an alternative notation for a computational logic and, as we show in this paper, are the basis of a visual logic programming language. The first implementation of this language and a heterogeneous logic programming environment are also presented in this paper.