SPICA's multi-party negotiation protocol : implementation using YAWL

A supply chain comprises several different kind of actors that interact either in an ad hoc fashion (e.g., an eventual deal) or in a previously well planned way. In the latter case, how the interactions develop is described in contracts that are agreed on before the interactions start. This agreement may involve several partners, thus a multi-party contract is better suited than a set of bi-lateral contracts. If one is willing to negotiate automatically such kind of contracts, an appropriate negotiation protocol should be at hand. However, the ones for bi-lateral contracts are not suitable for multi-party contracts, e.g., the way of achieving consensus when only two negotiators are haggling over some issue is quite different if there are several negotiators involved. In the first case, a simple bargain would suffice, but in the latter a ballot process is needed. This paper presents a negotiation protocol for electronic multi-party contracts which seamlessly combines several negotiation styles. It also elaborates on the main negotiation patterns the protocol allows for: bargain (for peer-to-peer negotiation), auction (when there is competition among the negotiators) and ballot (when the negotiation aims at consensus). Finally, it describes an implementation of this protocol based on Web services, and built on the YAWL Workflow Management System.