5.5.4 Generating Shared Team Beliefs

After the team-agent has added into its contents all the agents required

for the achievement of its initial commitment, the team-agent

may try to build the appropriate mutual beliefs among the team members.

The team-agent achieves this by sending appropriate messages to

its Contents, for example:

(5.9)

Bi

⎛

⎜⎜⎝

￢doing(i, book holiday)∧

capable(i, book hotel)∧

capable(i, book flight)∧

capable(i, rent car)

⎞

⎟⎟⎠

⇒

_

Tbelief (i, doing(i, book holiday))∧

Tbelief (i,♦done(book holiday))

_

(5.10)

Bidoing(i, book holiday)

⇒

⎛

⎝

Tbelief (i, doing(i, book hotel))∧

Tbelief (i, doing(i, book flight))∧

Tbelief (i, doing(i, rent car))

⎞

⎠

Now, when an agent receives a Tbelief message, it believes that the team

is undertaking the activity specified. This allows the agent to act, knowing

that certain activities are being performed elsewhere.

5.5.5 Team Computation

The team-members (the team-agent’s Contents), in order to be able to

start the execution of their particular part of the team’s joint task, need

to accommodate (something like) the following rule:

(5.11)

∀ x ∈ Contexts :

⎛

⎝

Tbelief (x, doing(σ))

∧ capable(i, σ)

∧ Bi(￢doing(i, σ)

⎞

⎠

⇒ request(i, σ) ∧ Bidoing(i, σ)

The team’s execution terminates either when all the individual tasks,

required for the achievement of the team-agent’s initial goal have been achieved, or when a particular team-member that plays a critical role

within the team drops its commitment to carry out the task that the team

has delegated to it.

In the first case, the appropriate rules that terminate the team are as

follows:

(5.12)

⎛

⎝

done(book flight)

∧ done(book hotel)

∧ done(rent car)

⎞

⎠ ∧ Bi￢done(book holiday)

⇒ Tbelief (i, done(book holiday))

In the second case we can either incorporate specific rules within the

team-agent’s description that will try to recover the situation or we can

simply terminate the team.

5.6 Summary

In this chapter, we have provided a review of work on executable specifications

based upon temporal and modal logics. In particular, we have

shown how such an approach might be productively used in the development

of simple organizational structures, such as teams.

5.6.1 Related Work

Teams are often viewed as groups of agents requiring their members

at least to have a joint goal and, possibly, to share some specific mental

properties such as intentions, beliefs and commitments, for example

[2, 21, 28]. Typically, an agent team is a group of agents working on

a common task having the ability to operate on dynamic environments

incorporating flexible coordination and communication facilities.

Simple groups of individual agents with prespecified coordination

plans in a very dynamic and continuously evolving domain will fail to

deliver due to inflexibility [28]. This is mainly because of the fact that it

is difficult to anticipate, and plan in advance for, all possible coordination

failures. Cohen and Levesque developed a framework for constructive

agent teamwork, taking into account the fact that teamwork is not

just the union of simultaneous actions carried out by the team’s members,

even if these actions are coordinated [2]. In their framework, they claim

that for flexible teamwork in real-time and highly dynamic domains, the

teams’ members have to share some certain mental features. They argue

that the mental notion of joint intention, which they formulate as a joint

commitment to perform a collective action while in a certain mental state,

serves as the glue that binds teams members together.

However, joint intention theory assumes that it is always possible to

attain mutual belief, and that once an agent comes to think the goal is

finished, it never changes its mind. Unfortunately, this may not always

be the case.

Another researcher who tried to addresses issues related with agent

teamwork is Tambe. Tambe’s model of teamwork is based on the notion

of hierarchical reactive plans and on a modified version of the joint intentions

theory [28] . The framework has been successfully applied in the

modeling of a soccer team [22], as well as in the modeling of intelligent pilots

in a battlefield simulator [28]. Tambe modifies joint intention theory

by: making communication conditional, rather than unconditional; and

enhancing mechanisms for dissolution of a joint commitment.

An attempt to model teamwork and, more generally, the cooperation

of agents for solving problems, is described by Wooldridge and Jennings

in [31]. The model represents the cooperation process from its beginning,

with some agent recognizing the potential for cooperation with respect to

one of its goals, through to team action that leads to the realization of this

goal.

It is important to note that we do not, in this chapter, attempt to model

the ideas of joint intentions/goals/beliefs in their full generality, but use a

combination of a logic of belief (TLBB), broadcast communication, and the

idea of representing groups as agents, in order to enforce common goals.

There is relatively little related work on executable agent specifications.

The main alternative approach is that of Golog [24] and Con-

Golog [17]. These are both based upon the Situation Calculus, in which

the preconditions for, and effects of, actions are specified. These actions

can be applied to situations (states) to generate new situations. In this

way, a sequence of actions can lead from an initial state to a goal state.

The typical way in which this is used in agents is to identify a goal state,

and then generate, via a planning process, a sequence of actions that will

transform the current/initial state into the goal state. This sequence of

actions is then executed by the agent. ConGolog is a multi-agent version

of Golog.