On the
Modeling, Refinement and Integration
of Decentralized Agent Coordination
– A Case Study on
Dissemination Processes in Networks
International Workshop on Self-Organizing Architectures (SOAR 09)
Cambridge, UK
Jan Sudeikat1,2 [email protected]
Wolfgang Renz1 [email protected]
1University
2University
of Applied Sciences Hamburg - Multimedia Systems Laboratory
Hamburg - Distributed Systems and Information Systems
Distributed Systems
and Information Systems
2009-03-25
Distributed Systems Architectures

Challenge:

Building adaptive applications that are scalable, robust, …
Architectural Choices:
Managed
Managing
Entity
Here:
Utilization of
Self-Organizing
Processes
Hierarchical
Decentral
Pyramid of
Managing
Entities
Scalability,
Robustness, …
 Local adaptive entities: software agents
 Problematic: effective coordination
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Self-Organization as a
(Software) Design Principle

Self-Organization:



physical, biological and social phenomena,
global structures arise from the local interactions
of autonomous individuals (e.g. particles, cells, agents, ...)
Structures are:

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Attractive for software architects:

Decentralized coordination strategies / mechanisms

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Adapted to changing environments
Maintained while being subject to perturbations
(Sudeikat & Renz 2008, 2009)
No single point of failure
Conceive application dynamics  resemble phenomena
Blending of functionality and coordination aspects (Reuse, Redesign)
Requirement: Systematic conception / integration


Declarative configuration of agent coordination
Enactment architecture
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Proposal:
Programming Model for Self-Organization

Self-organizing processes result from coupled
feedbacks between system elements


Context dependent
amplification / damping
of element activities
Systemic Modeling Approach

System Science concepts characterize MAS operation




…
System Variables: # behavior exhibitions (roles, groups, …)
Causal Relationships: rates of variable changes
 Feedback-Networks reinforcing / balancing
Toolset:
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
Configuration Language
Enactment Architecture
On the modeling, refinement and integration
of decentralized agent coordination
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(-)
(+)
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+
+
+
Distributed Systems
and Information Systems
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Coordination Enactment Architecture
Layered Approach
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Application
Coordination
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Coordination Media

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Interaction techniques
Agent-Modules
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Execution Infrastructure
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Coordination-Endpoint: Agent-modules
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Interface Coordination Media
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Publish / Subscribe mechanism
Automating coordination-activities
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1: Agent observation / modification
2: Controlled by coordination model
3: Publication of agent adjustments
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Externalized
Coordination
Model
Coordination Enactment Architecture
Coordination-Endpoint:
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Agent State Interpreter
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Observe agent execution
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Behavior-Classification
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Behavior-Change Publication
Coordination Information
Interpreter
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Reception via CM.
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Adjustment of agent-behavior
Local Adaptivity:
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Declarative: Conditions / Invariants
Adaptivity Component: (optional)
 Procedural Implementation of

Classification of Observations
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Adaptations of Agent state
Coordination Medium
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Publish / Subscribe Interface
On the modeling, refinement and integration
of decentralized agent coordination
Realizing self-organizing processes:
Information Flows
Local Element Adaptivity
Distributed Systems
and Information Systems
Methodic Conception of SO-Processes
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Integration of Coordination Development in AOSE
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AOSE: Tools / techniques for agent development
Plan for concerted phenomena
Systematic refinement procedure
Describing System Behavior
1. Identify Problem Dynamic


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Structures
Attractors
 coupled feedback loops
2. Propose Solution Dynamic
 Opposing / Corrective Structure
3. Refinement operations
 Map Coordination model to Agent models
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Case Study I: Convention Emergence
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Decentralized agreement problem in MAS
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Communication of local settings
Agents adjust accordingly
Embedding an externalized
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Generic agent activity
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Coordination Model:
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Convergence
Coordination Model
Observation of activities
Communication of configurations
 Adjustment
Policy: majority rule
+/- feedback loop
Coordination Medium: Overlay-Network Topology
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Case Study I: Convention Emergence
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Sample Simulation Run:
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Random Initialization
Value Convergence
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Random agent activation
Communication:
Coordination Medium
Impact of Network-Topology:
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Random Graph
Power law Graph:
Comparable convergence times
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Less communicative overhead
power law distributed graphs
On the modeling, refinement and integration
of decentralized agent coordination
in
Distributed Systems
and Information Systems
Case Study II: Patching Dynamics
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Exemplify refinement process:
Problem description  correcting coordination process
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Problem:
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Spreading of “infections”
in agent population
Agent exhibit two Roles:
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Susceptible
Infectious
Balancing vs. reinforcing Feedback  Goal-Seeking
Possible Solution Dynamic:
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Additional Balancing Feedback
Limit Susceptible and Infectious agents
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Case Study II: Patching Dynamics
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Refined Solution Dynamic
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Executable!
Adaptivity Component
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Functionality
Behavior Classification
Information Flow
Sample Simulation Run
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One random infection
Fixed infection rate
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infected
 Epidemic
Recovery of initial infection
starts recovering process
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
unsusceptible
Conclusions I
Embedding of self-organizing processes in MAS
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Architectural Aspect:
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Proposal:
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Supplement Coordination
Encapsulation of:
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Reference Architecture
Declarative language support
Adaptation logic
Information Flow / Interaction Technique
Methodic Aspect:

Equip self-organizing process to
correct / oppose problematic dynamics
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Conclusions II
“… how their contribution connects the self‐adaptive
perspective with the self‐organizing perspective”
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(System) Self-Adaptivity by concerted entity adaptivity
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Adaptive Software System:
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Establishment of closed feedback loop, e.g. MAPE, …
Here:
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Collective adjustments of individual elements
Closed feedback is distributed among system elements
System coordination model
On the modeling, refinement and integration
of decentralized agent coordination
Sets of feedback loops
Distributed Systems
and Information Systems
End
Thank you for your Attention!
Questions / Suggestions are welcome!
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Case Study I: Convention Emergence

Sample Simulation Run:


Random Initialization
Value Convergence



Random agent activation
Communication:
Coordination Medium
Impact of Network-Topology:



Random Graph
Power law Graph:
Comparable convergence times

Less communicative overhead
power law distributed graphs
On the modeling, refinement and integration
of decentralized agent coordination
in
Distributed Systems
and Information Systems
Encapsulating Adaptivity / Interaction
Foundational elements of a self-organizing processes
Information Flows
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Coordination Media:

Information exchange techniques
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Tuplespace, spatial environments,…
Here, Overlay-Network
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Local Element Adaptivity
Topology constraints communication
Coordination Endpoints:
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Local adpatation knowledge
Automation of coordination-related activities
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Coordination Pattern
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Systemic Software Modeling
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Modeling Notation
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Exemplifying Systemic Modeling of MAS
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Systemic Modeling
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Causal relations of system variables
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Anticipation of the
Qualitative System Dynamics
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Describe Entity behaviors
Manual inspection
and/ or simulation
A Hypothetical System:
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Producers  Products
Products  Storage
Storage  Production
Balancing
Feedback
Practical development:
After a suitable causal structure has been found:
How to implement ?
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
MASDynamics:
Declaration of Agent Behavior Interdependencies
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Systemic system model:
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Nodes  System Variables
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Node Types
# of groups
…
Link
Types
Interdependencies: Links
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# of role occupations
Direct:
 e.g. service invocations, …
Mediated:
 using environment models, e.g. pheromones, tuple spaces, …
Description levels:
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
Application independent
Alignment with agent implementation:
Nodes:
Links:
 Referencing reasoning events
 Configuring interaction techniques
that indicate behavior adjustments,
 E.g. environment models, …
 E.g. goal adoptions, plan activations, …
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Coordination Strategies
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Systemic Modeling of macroscopic dynamics
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Compensating
Amplifying
Selective
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Coordination Strategies

Systemic Modeling of macroscopic dynamics
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Compensating:
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Coordination Strategies

Systemic Modeling of macroscopic dynamics

Amplifying:
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Coordination Strategies

Systemic Modeling of macroscopic dynamics
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Selective:
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Decentralized Coordination Mechanisms
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Information Exchange techniques
Classification:
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Expressing Coordination Dynamics
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Structural Properties of SO-Systems
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Positive Feedback
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Negative Feedback
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Damping inappropriate entity activities
...
Dynamic Viewpoint on application development:
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Amplification of appropriate entity activities
Consider dyn. properties at design-time
Design the causes of self-organization
MAS specific modelling level:
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Agent-based design concepts:
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Roles: Abstraction of agent behaviours
Groups: sets of individuals that
share common characteristics
(e.g.: collective goals)
System State:

# of behaviour occupations
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Case Study:
Decentral Web-Service Management
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Agent-based Web-Service
Management Architecture
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Balance service workloads
Management Agents:
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(J2EE) Service-Endpoint
Broker Agents
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Registries: Service-Endpoints
Conceptual Architecture
Prototype Implementation:
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Jadex Agent Platform
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http://jadex.informatik.uni-hamburg.de/bin/view/About/Overview
Cognitive agent model  Beliefs, Goals, Plans, Internal Events, …
SUN Appserver Management Extensions (AMX)
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Server-Management Interface
https://glassfish.dev.java.net/javaee5/amx/
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Case Study:
Decentralized Web-Service Management
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A Functional, but un-coordinated
Implementation
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Manual management of is enabled
Tropos Modeling Notation
Dependencies of agent types
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Client
Client
Broker
Broker
 Service Endpoint
 Broker
 Service Endpoint
 Client
Systemic Description of the
Causal Application structure
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Tropos Design Notation
Accumulative system variables
Complementing the causalities
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Establish a negative feedback loop
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Agent state definitions
Establishment of interdependencies
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Case Study:
Decentralized Web-Service Management
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Embedding Coordination:
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Strategy Definition:
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Strategy alignment / integration
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Variable / Link Declarations
Referencing
agent models
Configuring
interaction technique
Validation:
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Event Publications
Provoking the manifestation
of the feedback loop
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Responsive regime
Event Perceptions
Sudden demand for
specific service type
Middleware Configuration
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Case Study: Behavioral Analysis by
Applying Stochastic Process Algebra
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Stochastic Process Algebra:
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Behavioral modeling
System of interacting processes
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Coupled by synchronized activities
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Validation of qualitative dynamic:
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Provoking the effects of
the feedback loop
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Responsive regime
Initial Conf.:
 Allocation of service 1
Input:
 High demand of service 2
Balance of allocations
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Mesoscopic Modeling
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Available formalisms:
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Macroscopic System
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Microscopic System
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Local entity (inter-)actions
State Machines, Process Algebra, …
Transition:
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System Sciences
Mathematics, …
Simulation / Iteration of microscopic models
Proposal: (Renz & Sudeikat, 2005, 2006)
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Mesoscopic agent states:
 Not microscopic:
Intermediate description levels:
 Coarse grained agent activities
Mesoscopic agent states
 Not macroscopic:
Classification of agent behaviors
 Exhibits short time fluctuations
 Relevance of agent activities with
respect to the Macroscopic System Behavior
 Abstraction of the microsopic agent activities
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Applying Mesoscopic Modeling
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Two orthogonal approaches:
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Different modeling directions
Enabling iterative development:
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Explain rising phenomena
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Tune rising phenomena
Top-Down:
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E.g.: MASDynamics
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Transfer of System
Dynamics concepts
Graph-based modeling
Bottom-up:
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E.g.: Stochastic
Situational Calculus

Extension of the Sit. Calculus
 modeling macroscopic
 coarse-graining element
dynamics
 refinement to
intermediate scales
dynamics
 inferring collective
system properties
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Top-Down: Systemic MAS Modeling

MAS abstraction by:

Agent-based design concepts:


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Roles: Abstraction of agent behaviours
Groups: sets of individuals that
share common characteristics
(e.g.: collective goals)
Global MAS State:


MAS Design
# of behaviour occupations
Graph Definition:

Nodes: System Variables

# of role occupations
 # of organizational groups
 size of organizational groups
 quantification of environment
elements ( #, size, etc. )
Links: Causal relations



Environment mediated
Direct agent interactions
On the modeling, refinement and integration
of decentralized agent coordination
Modelling the
causes of
Self-organization:
 Feedback Loop
Structures
Distributed Systems
and Information Systems
Top-Down: Systemic MAS Modelling

Allows for model refinement

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Attachment: add detail
Link: detail link dynamics
Variable: detail variable intern
dynamics
Example: Ant-based path finding
(-)
(+)
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems
Self-Organization vs. Emergence

Methodological view
On the modeling, refinement and integration
of decentralized agent coordination
Distributed Systems
and Information Systems