Bart: A specification language for bartering access to resources

Resource access management in modern ICT systems typically authorizes access based on attributes of the requester, the requested resource, and the environment. However, traditional access-control models are often inadequate in collaborative scenarios (such as social networks, research consortia, and smart-city IoT systems) where authorization may depend on reciprocal access requirements involving multiple parties. We introduce Bart, an attribute-based policy language for bartering access to resources in distributed and collaborative systems. Bart enables each party to specify local policies independently, while supporting explicit exchange conditions that may require mutually acceptable accesses to other resources before a request can succeed. Its evaluation process dynamically resolves these reciprocal requirements at runtime and handles circular dependencies through compliance-based cycle-breaking. Bart is equipped with a rigorously defined denotational semantics, which guided the design of a Java prototype for policy evaluation; we further establish the termination and decidability of request evaluation. We discuss the approach's applicability and assumptions, and assess its feasibility through realistic collaborative scenarios from different domains and performance experiments.