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Architectural Design of a Distributed Application with Autonomic Quality Requirements

This paper discusses the architectural design of a decentralized AGV transportation system that aims to cope with new quality requirements and deal with openness, flexibility, and adaptability. It presents a reference architecture for situated multiagent systems and explores the challenges and lessons learned in the project.

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Architectural Design of a Distributed Application with Autonomic Quality Requirements

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  1. Architectural Design of a Distributed Application with Autonomic Quality Requirements DEAS St. Louis, USA, May 21th, 2005 Danny Weyns, Kurt Schelfthout and Tom Holvoet University of Leuven, Belgium

  2. A challenging applicationAGV transportation system

  3. Traditional approach • Centralized architecture • Server assigns transports to AGVs • Server plans routes etc. • Vehicles are controlled by central server • Low level control AGVs is handled by E’nsor software • Main non-functional properties • Configurability (server is central configuration point) • Predictability (server manages execution of functionality)

  4. Aiming for new quality requirements • AGVs are expected to be flexible and adapt their behavior autonomously with changing circumstances • Exploit opportunities • Switch jobs when driving to a load when a more interesting transport pops up • Anticipate possible difficulties • Prefer jobs near to a battery charging station when battery needs to be charged in the near future • Cope with particular situations • Choose the farthest load in the corridor

  5. Aiming for new quality requirements • System is expected to deal with openness • AGVs leave/enter the system, e.g. for maintenance • 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

  6. Overview • Situated multiagent systems for the AGV transportation system • A trace through the architectural design • Round-up

  7. Situated multiagent systems • What is a situated multiagent system (MAS)? • Set of autonomous entities (agents) explicitly situated in a shared structure (an environment) • Agents select actions “here and now”, they do not use long term planning (locality in time and space) • Interaction is at the core of problem solving (rather than individual capabilities) Decentralized control Adaptive behavior Collective behavior

  8. A situated MAS for the AGV 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.

  9. Reference architecture for situated MASs • Reference architecture as a guidance for architectural design • Embodies knowledge and experiences acquired during 4 years of research • Serves as a reusable architectural design artifact • We developed design guidelines for specific modules, e.g., decision making with free-flow architectures

  10. High-level overview of the reference architecture

  11. Overview • Situated multiagent systems for the AGV transportation system • A trace through the architectural design • Round-up

  12. Deployment view of the decentralized architecture

  13. Top level module decomposition: situated MAS

  14. Module view of the environment: layers • Separate functionality, support reuse

  15. Virtual environment is a distributed entity

  16. Physical Environment

  17. Virtual Environment

  18. The virtual environment • Offers a medium to agents to exchange information and coordinate their behavior • Synchronizing state of the virtual environment • 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

  19. AGV agents:data repository • Separation of concerns, loose coupling

  20. AGV agents: blackboard with sequential processing • Decision making at different levels of abstraction, separation of concerns • Feedback for flexible decision making

  21. Overview • Situated multiagent systems for the AGV transportation system • A trace through the architectural design • Round-up

  22. The challenge continues • Project status (after 1.2 of 2 years) • 2 real AGVs manipulate loads, drive around and avoid collisions in an industrial test set-up (basics for deadlock prevention) • The same for n AGvs in a simulated setup • Current work • Methodological evaluation of software architecture: ATAM planned June • Order assignment and deadlock avoidance • Next challenges • Explore and validate flexibility, adaptability, scalability • Give guarantees about global behavior

  23. Lessons learned • We learned the real value of our research by applying it in real-world application • We experienced what “application-driven research” is about • The reference architecture serves as an excellent guidance for the architectural design • Stakeholders not involved in the daily development tend to overestimate the agent metaphor

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