Koen Hindriks, Birna van RiemsdijkMulti-agent systemen Multi-agent Systems & Coordination Maaike...

Koen Hindriks, Birna van Riemsdijk Multi-agent systemen

Multi-agent Systems & Coordination

Maaike HarbersDelft University of Technology, The Netherlands

Maaike Harbers,

Koen Hindriks, Birna van Riemsdijk Multi-agent systemenKoen Hindriks, Birna van Riemsdijk Multi-agent systemen

Outline

• Why do we need coordination in a multi-agent system (MAS)?

• What is coordination?

• How can we achieve coordination in a MAS?– Organizational structure– Conventions– Communication

• How can we use this in GOAL?

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Koen Hindriks, Birna van Riemsdijk Multi-agent systemenKoen Hindriks, Birna van Riemsdijk Kennistechnologie 2009-2010

Why do we need coordination?

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Examples of coordination

• Without coordination, what would happen here?

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http://www.wired.com/gadgetlab/2010/06/dance-dance-revolution-20-robots-think-they-can-dance/

• And what would

happen here?

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http://cacm.acm.org/news/98755-how-football-playing-robots-have-the-future-of-ai-at-their-feet/fulltext

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Coordination needed!

Environment

A1Agents A2

A3

A4

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What is coordination?

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Definitions of coordination

Coordination is... • ...managing dependencies between activities.

[Olson et al. 2001]

• ...the complementary temporal sequencing (or synchronicity) of behaviors among team members in the accomplishment of their goal. [Zalesny et al. 1995]

• ...to act in harmonious combination. [dictionary.reference.com]

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Joint activity

• Studying joint activity as defined by [Clark, 1996] provides a stronger basis for understanding coordination [Klein et al, 2005]

• A joint activity is an extended set of behaviors that are carried out by an ensemble of people who are coordinating with each other.

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Klein, G., Feltovich, P., Bradshaw, J. M., & Woods, D. D. (2005). Common ground and coordination in joint activity. Organizational Simulation. W. B. Rouse and K. R. Boff. New York City, NY, John Wiley.

Aspects of joint activity

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A. Criteria for joint activity

• Intention to generate a multi-party product• Different from what one person could do working alone

• Interdependence of the actions of the parties• Activities of parties interweave and interact

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A. Criteria: example

Making an assignment together• No intention – no assignment or two assignment• No interdepencence – each making one half of the

assignment without seeing the other half

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• Interpredictability

– Need to be able to accurately predict what others will do– Not just actions, but the coordination itself

• Common ground

– Pertinent mutual knowledge, beliefs, and assumptions about others’ skills and capabilities

– Joint activity is guided by signaling and coordination devices

• Directability

– Capacity for modifying the actions of the other parties as conditions and priorities change

– Responsiveness of each participant to the influence of the others

B. Requirements for joint activity

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Football team•Interpredictability – predict where team members will be on the field and who will be available

•Common ground – who is keeper, who defends, who attacks

•Directability – keeper tells others where to stand during acorner

B. Requirements: example

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C. Choreography of joint activity

• Three phases (functional breakdown)• coordinating tasks is coordinating subtasks• subtasks have an entry, body and exit phase

• Signaling transitions • within and between phases

• Coordination devices • serve to increase interpredictability• examples are organizational structure, convention, communication

protocol

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C. Choreography: example

Traffic•Three phase actions

- entering a road- being on the road- leaving a road

•Signaling transitions- turn signal

•Coordination devices- organizational structure, convention, communication protocol- to discuss…

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Using coordination devices

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Organizational structure

adapted from Bradshaw et al.


Organizational structure in BW4T

• Notion of ‘role’ is central

• Possible roles in BW4T? • searcher• deliverer• manager

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Conventions

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• A group of agents• Each agent is able to

solve the BW4T task individually

• Agents do not take into account that there are other agents

• What happens?

Conventions in BW4T

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• Do not enter rooms that are occupied• If you know about a block that can be delivered,

deliver that block• If someone intends to deliver a particular block, do

not try to deliver that block as well

Example of conventions in BW4T

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Conventions in organizational structure

Instructions of the manager should always be followed

If a searcher finds a block,

it must report that to the manager

adapted from Bradshaw et al.

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Communication

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• A group of agents• Each agent is able to

solve the BW4T task individually

• Agents take into account that there are other agents

• Agents do not communicate

• What happens?

Communication in BW4T

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Communication

• Communication can be regulated by conventions• Communication often related to roles• Communication protocols

• specify the rules of interaction between two or more communicating agents by restricting the range of allowed follow-up utterances for each agent at any stage during a communicative interaction (dialogue). [Endriss et al. 2004]

• sequence of related communicative acts

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BW4T communication protocol

• M = manager agent

• W = worker agent

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0 1 2 3

M: instruction W: update

M: new instruction

W: goal accomplished


How to use this in GOAL?

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How to Use This in GOAL? (1)

• functional breakdown (three phases)• breakdown of task in subtasks• which scheduling of these subtasks?

• organizational structure

• which roles can you identify?• which (hierarchical/peer-to-peer) relations between the roles?• when should agents change role and who decides this?

• conventions (for communication)

• when should agents communicate what?• which transitions should be signaled?• what (if anything) should agents reply to received messages?

Use as Design Guidelines for building your multi-agent systemUse as Design Guidelines for building your multi-agent system


How to Use This in GOAL? (2)

• functional breakdown• breakdown of task in subtasks module for each task➸• scheduling of subtasks action rules for entering (task) modules➸

• organizational structure

• identification of roles module for each role➸• relations between roles action rules for responding to requests➸• changing roles action rules for entering (role) modules➸

• conventions (for communication)• when communicate what action rules for sending messages➸• replies to messages from other agents action rules for sending messages ➸

with received message in mental state condition

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Pattern for Using Task Modules

• create module for each subtask

• define entering and exiting conditions

• use module option “exit=noaction”• define action rule for entering module

• implementation of the three phases

• action rules of module should implement task

• agent will exit module if no more actions can be executed; requires corresponding action selection strategy


Pattern for Using Role Modules

• create module for each role

• create entering and exiting policy• use module options “exit=nogoals” and “focus=select”• define action rule for entering module with goal query to

create focus of attention on goal of role• Example: if a-goal(delivered(1)) then deliverBlock.

module deliverBlock [exit=nogoals,focus=select] {...}

• action rules of module should aim at achieving goal of module

• agent will exit module if goal is reached


Emergency Exit

• There may be “emergency” circumstances in which to exit a module

• Task module• exiting module using exit-module action before

completing the task

• Role module

• exiting module by dropping the goal of the module/role using an action rule (because it should not be pursued anymore)

• exiting module using exit-module action (because goal of role should not be the current focus)


Study Goals: Coordination

Additional exam material:

• “Klein, G., Feltovich, P., Bradshaw, J. M., & Woods, D. D. (2005). Common ground and coordination in joint activity. (until section 4.4, p 1-16)

You should be able to:•Explain main notions•Apply notions to clarify joint activity in a concrete example

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Example question

“As part of my degree requirement we were supposed to do a research project in a group of 5 members. We had to write up a lengthy report and give a presentation within a four week deadline. My colleagues and I decided to split the work accordingly and decided to meet twice a week to give updates of our work and check on the groups progress as a whole making sure our work was in sync. Even though we had decided we would meet twice a week, I often had to email do call my colleagues to update them of my progress and find out how they were going on….”

•To what extent are the criteria for joint activity (intention and interdependence) satisfied in the above example of teamwork? Explain you answer.

•What is the organizational structure of the team described above, and what kind of role does the writer of this text play?

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Organisation

• Tutorial this week:– Assignment 4: team agent for BW4T

• Exam:– Specification of material to study will be posted on

blackboard– Example exams are available; however, be aware

that there is additional material this year– Possibly there will be several multiple choice

questions this year.

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Koen Hindriks, Birna van RiemsdijkMulti-agent systemen Multi-agent Systems & Coordination Maaike...

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