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Architectural Design of a Architectural Design of a Distributed Application with Distributed Application with

Autonomic Quality RequirementsAutonomic Quality Requirements

DEAS

St. Louis, USA, May 21th, 2005

Danny Weyns, Kurt Schelfthout and Tom Holvoet

University of Leuven, Belgium

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A challenging applicationA challenging applicationAGV transportation systemAGV transportation system

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Traditional approachTraditional approach

• Centralized architectureo Server assigns transports to AGVs

o Server plans routes etc.

o Vehicles are controlled by central server

o Low level control AGVs is handled by E’nsor software

• Main non-functional properties

o Configurability (server is central configuration point)

o Predictability (server manages execution of functionality)

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Aiming for new Aiming for new qualityquality requirements requirements

• AGVs are expected to be flexible and adapt their behavior autonomously with changing circumstances o Exploit opportunities

Switch jobs when driving to a load when a more interesting transport pops up

o Anticipate possible difficulties

Prefer jobs near to a battery charging station when battery needs to be charged in the near future

o Cope with particular situations

Choose the farthest load in the corridor

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Aiming for new Aiming for new qualityquality requirements requirements

• System is expected to deal with openness o AGVs leave/enter the system, e.g. for maintenance

o Customers intervene during execution of the system

We investigate the feasibility of a decentralized architecture aiming to cope with these new quality requirements

Joint R&D project between AgentWise research group and Egemin

This talk: overview basic architecture of the system

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OverviewOverview

• Situated multiagent systems for the AGV transportation system

• A trace through the architectural design

• Round-up

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Situated multiagent systemsSituated multiagent systems

• What is a situated multiagent system (MAS)? o Set of autonomous entities (agents) explicitly situated in a

shared structure (an environment)

o Agents select actions “here and now”, they do not use long term planning (locality in time and space)

o Interaction is at the core of problem solving (rather than individual capabilities)

Decentralized control

Adaptive behavior

Collective behavior

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A situated MAS for the A situated MAS for the AGV transportation systemAGV transportation system

• Motivations for situated MAS

• Matching quality properties

• Situated MAS are a promising approach to build flexible, adaptable, open systems

• Matching characteristics

Locality in time and space: order assignment to idle AGV near to load, collision avoidance, etc.

Interaction at the core of problem solving: load manipulation, collision avoidance, etc.

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3 • Reference architecture as a guidance for architectural designo Embodies knowledge and experiences acquired during

4 years of research

o Serves as a reusable architectural design artifact

o We developed design guidelines for specific modules, e.g., decision making with free-flow architectures

Reference architecture for Reference architecture for situated MASssituated MASs

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High-level overview of the reference High-level overview of the reference architecturearchitecture

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OverviewOverview

• Situated multiagent systems for the AGV transportation system

• A trace through the architectural design

• Round-up

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Deployment view of the Deployment view of the decentralized architecturedecentralized architecture

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Top level module decomposition: Top level module decomposition: situated MASsituated MAS

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Module view of the environment: Module view of the environment: layerslayers

Separate functionality, support reuse

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Virtual environment is a Virtual environment is a distributed entitydistributed entity

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Physical EnvironmentPhysical Environment

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Virtual Environment Virtual Environment

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AGV agent

Virtual environment

node

segment

hull projection

load

move cost

magnet strip Physical AGV

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The virtual environmentThe virtual environment

• Offers a medium to agents to exchange information and coordinate their behavior

• Synchronizing state of the virtual environment o Virtual environment as software entity does not exist

Virtual environment is necessary distributed over the AGVs

ObjectPlaces middleware keeps state of local virtual environment synchronized with virtual environments of local AGVs

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AGV agents:AGV agents:data repositorydata repository

Separation of concerns, loose coupling

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AGV agents: AGV agents: blackboard with sequential processingblackboard with sequential processing

Decision making at different levels of abstraction, separation of concerns

Feedback for flexible decision making

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OverviewOverview

• Situated multiagent systems for the AGV transportation system

• A trace through the architectural design

• Round-up

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The challenge continuesThe challenge continues

• Project status (after 1.2 of 2 years)o 2 real AGVs manipulate loads, drive around and avoid collisions

in an industrial test set-up (basics for deadlock prevention)

o The same for n AGvs in a simulated setup

• Current worko Methodological evaluation of software architecture: ATAM

planned June

o Order assignment and deadlock avoidance

• Next challenges o Explore and validate flexibility, adaptability, scalability

o Give guarantees about global behavior

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Lessons learnedLessons learned

o We learned the real value of our research by applying it in real-world application

We experienced what “application-driven research” is about

o The reference architecture serves as an excellent guidance for the architectural design

o Stakeholders not involved in the daily development tend to overestimate the agent metaphor