tion, the time frame of the negotiation, and the issues on which the negotiation is being conducted. The number of parties participating in the negotiation process can be two (bilateral negotiations) or more (multilateral negotiations). For example, in a market there can be one seller but many buyers, all involved in negotiating over a certain item. On the other hand, if the item is common, there may also be many sellers taking part in the negotiation process.

The negotiation environment also consists of a set of objectives and issues to be resolved. Various types of issues can be involved, including discrete enumerated value sets, integer-value

sets, and real-value sets. A negotiation consists of multi-attribute issues if the parties have to negotiate an agreement that involves several attributes for each issue. Negotiations that involve multi-attribute issues allow making complex decisions while taking into account multiple factors. 18 The negotiation environment can consist of non-coopera-tive negotiators or cooperative negotiators. Generally speaking, cooperative agents try to maximize their combined joint utilities (see Zhang40) while noncooperative agents try to maximize their own utilities regardless of the other sides’ utilities.

Finally, the negotiation protocol de-

figure 1. Variations of the negotiation settings.

H

G G: Diplomat

e
e: Guessing Heuristic
QOAgent

Virtual Human

f f: CT

D

c

Attributes

encounters

A A: Cliff-Edge

negotiators

B

B: AutONA

fines the formal interaction between the negotiators—whether the negotiation is done only once (one-shot) or repeatedly—and how the exchange of offers between the agents is conducted. A common exchange of offers model is the alternating offers model. 32 In addition, the protocol states whether agreements are enforceable or not, and whether the negotiation has a finite or infinite horizon. The negotiation is said to have a finite horizon if the length of every possible history of the negotiation is finite. In this respect, time costs may also be assigned and they may increase or decrease the utility of the negotiator.

Figure 1 depicts the different variations in the settings, along with the location of each system that is described in the section “Tackling the Challenges.” For example, point D in the cube represents bilateral negotiations with multi-attribute issues and repeated interactions, while point B represents multilateral negotiations with a single attribute for negotiation and a one-shot encounter.

The negotiation domain encompasses the negotiation objectives and issues and assigns different values to each. Thus, an agent may be tailored to a given domain (for example, the Diplomat agent22 described later is tailored to a specific domain of the Diplomacy game) or domain independent (for example, the QOAgent24 also described later).

 

figure 2. example of virtual humans’ negotiations.

The information model The information model dictates what is known to each agent. It can be a model of complete information, in which each agent has complete knowledge of both the state of the world and the preferences of other agents; or it can be a model of incomplete information, in which agents may have only partial knowledge of either the states of the world or the preferences of other agents (for example, bargaining games with asymmetric information), or they may be ignorant of the preferences of the opponents and the states of the world. 33 The incomplete information can be modeled in different ways with respect to the uncertainty regarding the preferences of the other party. One approach to modeling the information is to assume that there is a set of differ-