On the Expressiveness of Attribute Global Types: The Formalization of a Real Multiagent System Protocol

Attribute global types are a formalism for specifying and dynamically verifying multi-party agent interaction protocols. They allow the multiagent system designer to easily express synchronization constraints among protocol branches and global constraints on sub-sequences of the allowed protocol traces. FYPA (Find Your Path, Agent!) is a multiagent system implemented in Jade currently being used by Ansaldo STS for allocating platforms and tracks to trains inside Italian stations. Since information on the station topology and on the current resource allocation is fully distributed, FYPA involves complex negotiation among agents to find a solution in quasi-real time. In this paper we describe the FYPA protocol using both AUML and attribute global types, showing that the second formalism is more concise than the first, besides being unambiguous and amenable for formal reasoning. Thanks to the Prolog implementation of the transition function defining the attribute global type semantics, we are able to generate a large number of protocol traces and to manually inspect a subset of them to empirically validate that the protocol's formalization is correct. The integration of the Prolog verification mechanism into a Jade monitoring agent is under way.