A Recursive Protocol for Negotiating Contracts Under Non-monotonic Preference Structures

Abstract

Negotiating contracts with multiple interdependent issues may yield non-monotonic preference spaces for the participating agents. These negotiations are specially challenging because of the complexity and dimension of the search space. Automated negotiation mechanisms designed and proven useful for monotonic utility spaces may fail in these negotiation scenarios. This paper presents a novel solution to the problem of automated multi-issue negotiations in the context of complex utility spaces. We seek to address the challenge of intractably large contract spaces and utility functions with multiple local optima in automated negotiation scenarios. A protocol for automated bilateral multi-attribute negotiation processes is proposed, in which the individual agents’ preferences can be non-monotonic and discontinuous. The protocol is based on a recursive non-mediated bargaining mechanism, which involves two agents who simultaneously exchange proposals defined as regions within the negotiation space. An agreement on a region implies a new bargaining which is restricted to that region. This recursive process is governed by a set of rules which modulate the joint exploration of the negotiation space until an agreement is found or a deadline expires. The protocol is experimentally evaluated under monotonic and non-monotonic preference scenarios, confirming that the protocol is able to produce outcomes close to the Pareto frontier in acceptable negotiation time, outperforming previous approaches.