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Jan Sudeikat1,2 [email protected]
Wolfgang Renz1 [email protected]
1University of Applied Sciences Hamburg - Multimedia Systems Laboratory 2University Hamburg - Distributed Systems and Information Systems
Distributed Systemsand Information Systems
On the Modeling, Refinement and Integration
of Decentralized Agent Coordination– A Case Study on
Dissemination Processes in Networks
2009-03-25
International Workshop on Self-Organizing Architectures (SOAR 09)
Cambridge, UK
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Distributed Systems Architectures
Challenge: Building adaptive applications that are scalable, robust, …
Architectural Choices: Managed Hierarchical
Decentral
Local adaptive entities: software agents Problematic: effective coordination
Here:Utilization of
Self-Organizing Processes
Scalability,Robustness, …
Managing Entity
Pyramid of Managing
Entities
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand 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:
Adapted to changing environments Maintained while being subject to perturbations
Attractive for software architects: Decentralized coordination strategies / mechanisms
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
(Sudeikat & Renz 2008, 2009)
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand 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
Toolset: Configuration Language Enactment Architecture
…
+(+)
reinforcing
+
++
+
(-)+
++
-/ balancing
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Coordination Enactment Architecture
Layered Approach Application Coordination
Coordination Media Interaction techniques
Agent-Modules Execution Infrastructure
Coordination-Endpoint: Agent-modules Interface Coordination Media
Publish / Subscribe mechanism Automating coordination-activities
1: Agent observation / modification 2: Controlled by coordination model 3: Publication of agent adjustments
Externalized Coordination
Model
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Coordination-Endpoint: Agent State Interpreter
Observe agent execution Behavior-Classification Behavior-Change Publication
Coordination Information Interpreter
Reception via CM. Adjustment of agent-behavior
Local Adaptivity: Declarative: Conditions / Invariants Adaptivity Component: (optional) Procedural Implementation of
Classification of Observations Adaptations of Agent state
Coordination Medium Publish / Subscribe Interface
Coordination Enactment Architecture
Realizing self-organizing processes: Information FlowsLocal Element Adaptivity
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Methodic Conception of SO-Processes Integration of Coordination Development in AOSE
AOSE: Tools / techniques for agent development Plan for concerted phenomena
Systematic refinement procedure Describing System Behavior1. Identify Problem Dynamic
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 integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Case Study I: Convention Emergence
Decentralized agreement problem in MAS Communication of local settings Agents adjust accordingly
Embedding an externalized Coordination Model Generic agent activity
Coordination Model: Observation of activities Communication of configurations Adjustment Policy: majority rule
+/- feedback loop Coordination Medium: Overlay-Network Topology
Convergence
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand 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 in power law distributed graphs
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Case Study II: Patching Dynamics
Exemplify refinement process: Problem description correcting coordination process
Problem: Spreading of “infections”
in agent population Agent exhibit two Roles:
Susceptible Infectious
Balancing vs. reinforcing Feedback Goal-Seeking
Possible Solution Dynamic: Additional Balancing Feedback Limit Susceptible and Infectious agents
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Case Study II: Patching Dynamics
Refined Solution Dynamic Executable! Adaptivity Component
Functionality Behavior Classification
Information Flow
Sample Simulation Run One random infection Fixed infection rate
Epidemic Recovery of initial infection
starts recovering process
unsusceptibleinfected
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Conclusions I
Embedding of self-organizing processes in MAS
Architectural Aspect: Proposal:
Reference Architecture Declarative language support
Supplement Coordination Encapsulation of:
Adaptation logic Information Flow / Interaction Technique
Methodic Aspect: Equip self-organizing process to
correct / oppose problematic dynamics
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Conclusions II
“… how their contribution connects the self‐adaptiveperspective with the self‐organizing perspective”
(System) Self-Adaptivity by concerted entity adaptivity Adaptive Software System:
Establishment of closed feedback loop, e.g. MAPE, … Here:
Collective adjustments of individual elements Closed feedback is distributed among system elements
System coordination model Sets of feedback loops
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
End
Thank you for your Attention!
Questions / Suggestions are welcome!
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand 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 in power law distributed graphs
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Encapsulating Adaptivity / Interaction
Foundational elements of a self-organizing processes Information Flows Local Element
Adaptivity
Coordination Media: Information exchange techniques
Tuplespace, spatial environments,… Here, Overlay-Network
Topology constraints communication
Coordination Endpoints: Local adpatation knowledge Automation of coordination-related activities
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Coordination Pattern
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Systemic Software Modeling
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Modeling Notation
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Systemic Modeling Causal relations of system variables
Describe Entity behaviors Anticipation of the
Qualitative System Dynamics Manual inspection and/ or simulation
A Hypothetical System: Producers Products Products Storage Storage Production
Exemplifying Systemic Modeling of MAS
Balancing Feedback
Practical development: After a suitable causal structure has been found:How to implement ?
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
MASDynamics: Declaration of Agent Behavior Interdependencies
Systemic system model: Nodes System Variables
# of role occupations # of groups …
Interdependencies: Links Direct:
e.g. service invocations, … Mediated:
using environment models, e.g. pheromones, tuple spaces, … Description levels:
Application independent Alignment with agent implementation:
Node Types LinkTypes
Nodes: Referencing reasoning events that indicate behavior adjustments, E.g. goal adoptions, plan activations, …
Links: Configuring interaction techniques E.g. environment models, …
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Coordination Strategies
Systemic Modeling of macroscopic dynamics Compensating Amplifying Selective
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Coordination Strategies
Systemic Modeling of macroscopic dynamics Compensating:
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Coordination Strategies
Systemic Modeling of macroscopic dynamics Amplifying:
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Coordination Strategies
Systemic Modeling of macroscopic dynamics Selective:
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Decentralized Coordination Mechanisms
Information Exchange techniques Classification:
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Expressing Coordination Dynamics
Structural Properties of SO-Systems Positive Feedback
Amplification of appropriate entity activities Negative Feedback
Damping inappropriate entity activities ...
Dynamic Viewpoint on application development: Consider dyn. properties at design-time Design the causes of self-organization
MAS specific modelling level: Agent-based design concepts:
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 integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Case Study: Decentral Web-Service Management
Agent-based Web-Service Management Architecture
Balance service workloads Management Agents:
(J2EE) Service-Endpoint Broker Agents
Registries: Service-Endpoints
Prototype Implementation: Jadex Agent Platform
Cognitive agent model Beliefs, Goals, Plans, Internal Events, …
SUN Appserver Management Extensions (AMX) Server-Management Interface
Conceptual Architecture
http://jadex.informatik.uni-hamburg.de/bin/view/About/Overview
https://glassfish.dev.java.net/javaee5/amx/
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Case Study: Decentralized Web-Service Management
A Functional, but un-coordinated Implementation
Manual management of is enabled Tropos Modeling Notation Dependencies of agent types
Client Service Endpoint Client Broker Broker Service Endpoint Broker Client
Systemic Description of the Causal Application structure
Accumulative system variables
Complementing the causalities Establish a negative feedback loop
Agent state definitions Establishment of interdependencies
Tropos Design Notation
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Case Study: Decentralized Web-Service Management
Embedding Coordination: Strategy Definition:
Variable / Link Declarations Strategy alignment / integration
Referencing agent models
Configuring interaction technique
Validation: Provoking the manifestation
of the feedback loop Responsive regime Sudden demand for
specific service type
Event Publications
Event Perceptions
Middleware Configuration
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Case Study: Behavioral Analysis by Applying Stochastic Process Algebra
Stochastic Process Algebra: Behavioral modeling System of interacting processes Coupled by synchronized activities
Validation of qualitative dynamic: Provoking the effects of
the feedback loop Responsive regime Initial Conf.:
Allocation of service 1 Input:
High demand of service 2
Balance of allocations
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Mesoscopic Modeling
Available formalisms: Macroscopic System
System Sciences Mathematics, …
Microscopic System Local entity (inter-)actions State Machines, Process Algebra, …
Transition: Simulation / Iteration of microscopic models
Proposal: (Renz & Sudeikat, 2005, 2006) Intermediate description levels: Mesoscopic agent states Classification of agent behaviors
Relevance of agent activities with respect to the Macroscopic System
Behavior Abstraction of the microsopic agent activities
Mesoscopic agent states: Not microscopic:
Coarse grained agent activities Not macroscopic:
Exhibits short time fluctuations
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Applying Mesoscopic Modeling
Top-Down: E.g.: MASDynamics
Transfer of System Dynamics concepts
Graph-based modeling
Bottom-up: E.g.: Stochastic Situational Calculus
Extension of the Sit. Calculus
Two orthogonal approaches: Different modeling directions Enabling iterative development:
Explain rising phenomena Tune rising phenomena
modeling macroscopic dynamics refinement to intermediate scales
coarse-graining element dynamics inferring collective system properties
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Top-Down: Systemic MAS Modeling
MAS abstraction by: Agent-based design concepts:
Roles: Abstraction of agent behaviours Groups: sets of individuals that
share common characteristics (e.g.: collective goals)
Global MAS State: # 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
Modelling the causes of Self-organization: Feedback Loop Structures
MAS Design
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Top-Down: Systemic MAS Modelling
Allows for model refinement Attachment: add detail Link: detail link dynamics Variable: detail variable intern
dynamics
Example: Ant-based path finding
(-)
(+)
On the modeling, refinement and integrationof decentralized agent coordination
Distributed Systemsand Information Systems
Self-Organization vs. Emergence
Methodological view
