A Nonmonotonic Delegation Logic with Prioritized Conflict Handling

We extend previous work on Delegation Logic (DL) [11, 12], a tractable and practically implementable logic-based language for authorization in large-scale, open, distributed systems. We expressively generalize the previous version of DL (called D1LP) to have nonmonotonic expressive features, including negation-as-failure, classical negation, and prioritized conflict handling. The resulting formalism is called D2LP. We discuss the motivations and usefulness of prioritized conflict handling and some subtleties and challenges in extending DL to have it. Partly because of these subtleties, in this paper we restrict D2LP by prohibiting queries about delegation statements. Our technical approach to defining D2LP is based on tractably compiling a D2LP into a Generalized Courteous LP (GCLP) [7, 8], which is in turn tractably compiled into an Ordinary LP (OLP). We show that D2LP is thus tractable and practically implementable on top of existing technologies for OLP, e.g., Prolog, SQL databases, and other rule-based systems.