A practically implementable and tractable delegation logic

We address the goal of making Delegation Logic (DL) into a practically implementable and tractable trust management system. DL (N. Li et al., 1999) is a logic based knowledge representation (i.e., language) for authorization in large scale, open, distributed systems. DL inferencing is computationally intractable and highly impractical to implement. We introduce a new version of Delegation Logic that remedies these difficulties. To achieve this, we impose a syntactic restriction and redefine the semantics somewhat. We show that, for this revised version of DL, inferencing is computationally tractable under the same commonly met restrictions for which Ordinary Logic Programs (OLP) inferencing is tractable (e.g., Datalog and bounded number of logical variables per rule). We give an implementation architecture for this version of DL; it uses a delegation compiler from DL to OLP and can modularly exploit a variety of existing OLP inference engines. As proof of concept, we have implemented a large expressive subset of this version of DL, using this architecture.