We present a visual language expressive enough to capture an important subset of First Order Predicate Logic as well as its straightforward translation to the logic-based paradigm of deductive databases. We use the diagrams of our language to represent all the components of a deductive database schema: base predicates, derived predicates with their deductive rules, and integrity constraints. Our diagrams are grounded on two powerful visual metaphors: Venn/Euler diagrams and graphs, familiar to most designers; they are formal and independent of the application domain; they emphasize basic forms of logic description, the diagrammatic syntax being closer to the semantics; and they have a simple translation to Horn clauses. Thus, we aim at a situation where the generality of deductive databases would be fostered by the expected greater usability of visual schema languages in the hands of a wider group of practitioners.