A practical module system for logic programming and its semantics

Encapsulation constructs with import/export declarations is the structuring facility offered in most commercial Prolog systems. However, real-life applications have shown to require a finer information exchange between encapsulated pieces of code. A refinement of import/export declarations for logic modules is presented both as a stricter form of communication between the modules and as a larger variety of visibility states of the predicates, the standard approaches being special cases of it. The semantics of this module system has been examined and model-theoretic, fixpoint and operational ones have been given and have been proved to be equivalent. In addition, the module system has been naturally transformed to Horn clause logic