From queries to answers in visual logic programming

Previously (J. Puigsegur et al., 1996), we presented a visual declarative programming language based on two main graphical constructs: directed acyclic graphs representing predicate application and graphical set inclusion representing logical implication. We showed that with these simple visual constructs we can cover most of the representational demands of computational logic allowing a blend of functional and relational styles of programming. We explore the advantages of directly using our visual syntax for solving queries, by presenting a method for visually asking questions about a visual program by means of query diagrams, and by defining visual inferences which operate on those diagrams. The result is an operational semantics for declarative programming which is intended to be visual, intuitive and formal. Visual, because the inference rules display graphically the transformation of query diagrams into answer diagrams. Intuitive, because it is intimately linked with the visual syntax of the declarative language. Finally, it is formal because the usual properties of formal logic (i.e. correctness and completeness) can be applied directly to it.