Towards a Simulation Tool for Towards a Simulation Tool for Evaluating Dynamic Evaluating Dynamic

Reorganization of Agent Reorganization of Agent SocietiesSocieties

V. Dignum, F. Dignum, Utrecht UniversityL. Sonenberg, University of MelbourneV. Furtado, A. Mello, University of Fortaleza

OutlineOutline

Main issues Motivation Organizations and change Reorganization typology Reorganization requirements The VILLA simulation environment Conclusions

Main issues in Main issues in ReorganizationReorganization

1. When2. Why 3. What

• Behavior• Structure

4. Who5. How

• External to system: re-design• Within system: dynamic

– Decision, authority

MotivationMotivation

Need for organization– Stability– Cope with uncertainty

Need for reorganization– Answer to change

• environment, objectives, population

– Flexibility

Need for reorganizationNeed for reorganization

Need for organization: achieve stability

Reorganization means loss of stability Need for reorganization

– Answer to environment changes– Answer to population changes– Answer to objective changes

Reorganization decision depends on – organizational utility and success.– individual utility and success

Organizational UtilityOrganizational Utility

Organizational Success: ability to bring assets to bear, recognize and take advantage of opportunities.– Ex: MAS perspective

• Interaction success: how often result in desired aim?• Role success: how often agents achieve role goals?• Structure success: how well are global goals

achieved?• Combined utilities of agents in organization

Utility: determined based on– Current success – Expected success– Cost of reorganization

Individual UtilityIndividual Utility

Success and utility are different for each agent– Dependent on own goals and

resources– Dependent on social attitude

Role utility to agent success determines participation in organization

Moments of reorganization – Moments of reorganization – when and why?when and why?

From organizational theory Timing (timeliness)

– Proactive: prepare for expected change

– Reactive: adjust after change Intention (resiliency)

– Offensive: gain advantage– Defensive: ensure survival

[Evans, 1991]

Reorganization manouvresReorganization manouvres

Intention

Tim

ing

pre-emptive-Expected future-Competition through innovation

offensive defensive

react

ive

pro

act

ive

protective-Expected future-Limit damages

exploitive-Taken after event-Capitalize opportunities

corrective-Taken after event-Prevent more damage-Ensure continuity

Focus of Reorganization – Focus of Reorganization – what?what?

Behavior change– Temporary, ‘local’ to one population– A new agent joins the MAS– An agent leaves the MAS– Interaction pattern instantiation

Structural change– Permanent, valid across populations– Organizational Self Design– Structural Adaptation

Means for reorganization – Means for reorganization – how?how?

Decision– concerns how reorganization

decisions are reached.– Relates to the decision-making style.

Authority– Concerns what aspects can be

changed by who in the organization– Relates to the C2 Model

Reorganization Decision – Reorganization Decision – who?who?

Externally imposed– Agents have no influence on reorganization – occurs through system redesign

Role based– Command-driven: the agent does not make any

decisions on how to pursue its goals, and some other agent has authority over it

– Locally autonomous/master: The agent makes decisions alone and may or not have control over other agents

True consensus – Agent works as a team member, sharing decision

making control equally with other agents

[Barber, Martin, 2001]

Reorganization Authority – Reorganization Authority – what?what?

C2 Model– Command: authority and responsibility to

determine the objectives of the organization. Can update the social structure of the organization.

– Control: authority to specify and modify detailed plans for achieving objectives. Authority to modify interactions and behavior.

C3 Model: C2 plus– Communications: collection and sharing

information about the environment, the state of the organization, the state of the achievement of objectives, and the state of execution of the plans.

• Meta-communication [Galey, 1987, Tidhar, Sonenberg, 2001]

Dynamic reorganization Dynamic reorganization stylesstyles

Authority

Deci

sion

Shared control

Shared command

Role-basedcontrol

Role-basedcommand

Behavior Structure

dir

ect

ive

colla

bora

tive

Requirements for Requirements for reorganizationreorganization

Observation– Identify patterns– Evaluate current response

possibilities– Generate options, predict outcomes,

understand effects Organizational requirements Agent capabilities

Organizational Organizational requirementsrequirements

Reorganization success– Timeliness– Adaptance/consensus– Resiliency

Depend on organizational form/domain– Hierarchy: role-based reorganization

decision?– Network: shared reorganization decision?– Market: favors behavior change?

Agent capabilitiesAgent capabilities

Authority

Deci

sion

Shared Control• no memory• reasoning• meta-communication

Behavior Structure

dir

ect

ive

colla

bora

tive

Shared Command• memory• reasoning• meta-communication

Role-based control• no memory• reasoning: only role• no meta-communic.

Role-based Command

• memory: only role• reasoning: only role• no meta-communic.

Simulation Aims - 1Simulation Aims - 1

Full theory of reorganization is more than what can be studied in one simulation

Agent behavior depends on– Own state and environment state– But also on the organizational structure– Organizational structure is thus not just a

component of the environment Organizational elements considered:

– Type of goal (simple to complex)– Roles (many agents, one agent)– Interactions (communication protocols, dole

dependencies)

Simulation Aims - 2Simulation Aims - 2

1. Identify match of organization structure to environment characteristics

2. Adaptation to (drastic) changes– Structural vs. behavioral– Role-directed vs. collaborative

3. Communication requirements to reason about change

– Also, reasoning with limited knowledge

The VILLA environmentThe VILLA environment

Aim: community survival Creatures

– Gatherers: can collect (limited) food individually

– Hunters: can hunt (large amounts of) food in groups

– Others: consume food, can grow to become Gatherers or Hunters

– Head: observe and change society

VILLA: ActivitiesVILLA: Activities

Simulation takes a number of runs (days)

In each run:– Eat

• If food available• Collectors eat more than others• If not eat, health decreases• If health = 0, then creature dies

– Collect• Gatherers: individual function on health• Hunters: groups’ function on health and size

– Move• Hunters must move to form group

VILLA setupVILLA setup

VILLA without VILLA without reorganizationreorganization

Evaluation of VILLAEvaluation of VILLA

Influences on health:– Role typology– Role capabilities

Results from evaluation of non reorganization situation:– Food stack decreases a lot at beginning– Need to introduce delay in adaptation– Others average health seems to be good

indicator for reorganization– Need to evaluate time interval, not time

point

Evaluation of VILLA (no Evaluation of VILLA (no reorg)reorg)

G H O Comments17 0 0 Gatherers survive with 100% of health. 6 11 0 All creatures die because amount of food is not sufficient to keep a

good health level. 0 9 8 All creatures die. Only in cases when the hunters get together very

early some creatures survive. Hunters keep others alive if food stack is very high (more than 10000)

0 17 0 All creatures survive more than 100 TICs. However, food stack must be 900 to allow Hunters to get together within 500 ticks.

9 8 0 Very good society but depends on the probability of Hunters to get together.

8 5 4 Stable society with health 80%. However some Others will die.8 6 3 Stable society with health 80%. However some Others will die.8 6 2 Good and stable society with health greater than 80%7 5 4 All creatures die7 7 3 All creatures die7 3 7 All creatures die9 5 3 Very good society9 6 2 Good society9 7 1 Very good society with health 95% but instable if Hunters are isolated.6 10 1 Very good society with health in 95% but instable if Hunters are

isolated.5 11 1 Very good society with health in 95% but instable if Hunters are

isolated.4 11 2 Good society but very instable if Hunters are isolated.3 11 3 Good society but very instable if Hunters are isolated.

Evaluation of VILLA (no Evaluation of VILLA (no reorg)reorg)

G H O Prob. Gather

Prob. Hunter

Comments

9 5 3 9 10 Instable Society, depending on hunters’ aggregation.

9 6 2 9 10 Instable Society, depending on hunters’ aggregation.

9 5 3 15 18 Stable society independent of hunters aggregation. Reach 100% and food stack increase.

9 6 2 15 18 Stable society independent of hunters aggregation. Reach 100% and food stack increase.

9 0 8 15 18 Stable society independent of hunters aggregation. Reach 100% and food stack increase.

5 0 12 15 18 Minimum number of gatherers for supporting other life.

0 17 0 15 18 With the increasing of prob. Hunters always still alive and keep society good

8 5 4 15 18 Health society before was 80% now 100%.

7 7 3 15 18 Stable society independent of hunters aggregation. Reach 100% and food stack increase.

7 6 4 15 18 100% “

7 5 5 15 18 100% ”

7 5 5 18 20 100%

Reorganizing SocietiesReorganizing Societies Behavioral change:

– If food stack < 250, increase gather power by 1

– Reorganization delay is 100

Reorganizing SocietiesReorganizing Societies Structural change:

– If food stack < 250, create 1 gatherer (from Others)

– Reorganization delay is 100

ConclusionsConclusions

First step towards a model of reorganization

Identification of characteristics of reorganization

Requirements for reorganization– Different organizational types– Challenges for agent capabilities

Future workFuture work

Empirical study – How systems react to different

reorganization forms– Further evaluation/development of VILLA

Reorganization methodology– Conditions and requirements– Determine choices

Formal model for reorganization? – Organizational utility– Reorganization cost