A Mobile Agent Approach to Process-based Dynamic Adaptation of Complex Software Systems

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A Mobile Agent Approach to Process-based Dynamic
Adaptation of Complex Software Systems

• Gail Kaiser
• Columbia University

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Dynamic Adaptation

• Modifications in structure and behavior that can
  be made to individual components, as well as sets
  thereof, or to the overall target system
  configuration, such as adding, removing or
  substituting components, while the system is
  running and without bringing it down.
• Goals
• Supporting run-time software composition,
• Enforcing adherence to requirements,
• Ensuring uptime and quality of service of
  mission-critical systems,
• Recovering from and preventing faults,
• Seamless system upgrading, etc.

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Our Approach

• Dispatch mobile agents to components to perform
  dynamic adaptation tasks
• Coordinate concerted action of multiple agents on
  multiple components via decentralized workflow
• Dynamic adaptation workflow process incorporates
  knowledge about the specifications and
  architecture of the target software system
• Allows to address at runtime configuration
  management, deployment, validation and evolution
  concerns normally dealt with only at development
  time

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Prerequisite Infrastructure

• Superimpose a minimally intrusive monitoring
  meta-architecture on top of the target system
• Introduce an adaptation feedback and feedforward
  control loop onto the target system, detecting
  and responding to the occurrence of certain
  conditions at and among components and connectors
• Contrasted to fine-grained internal diagnostics
  and remedies performed in isolation by a
  self-assured, fault-tolerant component, aims to
  handle more global situations, perhaps involving
  heterogeneous components obtained from multiple
  sources (COTS, open source)

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Kinesthetics eXtreme (KX)

• Probes register and report low-level events
  indicating the behaviors/activities (or lack
  thereof) of the target system (via active
  interfaces, probelets, instrumented connectors,
  others)
• Distributed asynchronous event bus receives
  probed events and propagates them
  (publish/subscribe) through packaging, filtering
  and notification facilities
• Gauges describe/measure the progress of the
  target system, rendered as visual or textual
  portal panels or as data feeds into decision
  support

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Kinesthetics eXtreme (KX)

• Decision agents (human or automated) respond to
  gauged conditions by determining appropriate
  target system adaptations
• Workflow engine
• Actuation facilities deliver and execute any
  adaptation procedures
• Worklets (aka Gaugents)

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Worklets

• Mobile software agents support micro-workflow
• Contain one or more mobile code units worklet
  junctions
• Worklet transparently travels from host to host,
  dropping off and picking up junctions
• Optional origin junction returns the worklet to
  originating host

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Worklet Virtual Machine (WVM)

• Generic worklet execution platform
• Middleware interfaces to each host through
  host-specific adaptor
• Tradeoff between adaptor complexity and worklet
  specialization
• 1st JPython scripted worklets, heavyweight
  adaptor implemented std API
• 2nd Java coded worklets, lightweight adaptor
  specialized to domain/application/etc.

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Worklet flow
A D A P T O R
A D A P T O R1
A D A P T O R2
H O S T1
H O S T2
WVM
WVM
WVM
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Workflakes Managing Micro- and Macro-Workflow

• Worklets deliver junctions wrapped in worklet
  jackets - scripted triggers, pre-conditions and
  timing for activation and repetition, exit
  conditions, directives to supersede, suspend, and
  reactivate a junction upon delivery of another,
  etc. (micro-workflow)
• Workflakes decentralized workflow engine emits
  and coordinates multiple (jacketed) worklets
  collectively realizing the dynamic adaptation
  process (macro-workflow)

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Separation of Concerns

• Worklet junctions define and execute computations
• Workflow modeling language defines and
  decentralized workflow engine enacts coordination
• Specify (conditional) worklet trajectory
• Generate worklet jackets
• Select and instantiate worklet junctions from
  worklet factory

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Process Repository
Probe
T A R GET

• Process
• Fragment

J A C K E T
Worklet Transport
WVM
Junctions Catalogue
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Example Application Adaptive Interactive
Internet Team Video

• Multimedia-enhanced group distance learning and
  collaborative work
• Dispersed teams of students
• Review recorded lecture videos together
• Interactively carry out course assignments
• Different teams members have different computing
  and networking capabilities
• But need to view the semantically same thing at
  physically same time

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AI2TV Approach

• Semantics-based video segmentation, indexing and
  compression (Prof. Kender)
• Specialized mpeg encoder/decoder adapts to
  resource availability (Prof. Nieh)
• KX monitors multimedia synchronization and
  continually updates gauges
• Workflakes directs dynamic adaptation performed
  by worklets
• Workflow model also guides predictive video
  segment caching (prefetching) based on team
  agendas

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Multiple Workflow Levels

• Application-level
• Coordination of group work (traditional)
• Multimedia provision follows team agendas
• Control-level
• Process-aware components (via WVM adaptors)
• Adapts behavior of the infrastructure (caching,
  streaming, resource management, etc.)
• Reflective
• Dynamically adapt KX continual validation
• Smart Event vocabulary, complex event patterns,
  event matching and processing

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KX
Controls
Controls
Controls
Controls
Controls
Controls
Controls
Controls
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Worklets 2.0

• Java 1.3
• Can push (payload) or pull (RMI or URL
  ClassLoader) mobile code
• Download from http//www.psl.cs.columbia.edu/softw
  are/download/

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Workflakes 0.5?

• Initial experiment with Little-JIL/Juliette
  (UMass)
• Little-JIL workflow modeling notation
• Hierarchical workflow breakdown with coordination
  relationships and qualifiers among tasks
• Sub-hierarchies assigned to decentralized
  processors (Juliette agents)
• Juliette decentralized workflow enactment
• Mockup of Juliette AutomatedAgent
• Manages agenda and sends worklets to execute leaf
  tasks
• Cougaar-based implementation (DARPA) under way
• Logistics workflow (worklet dispatch treated as a
  logistics problem)
• Adaptable to other workflow paradigms
• Shell generic Cougaar task processor is filled
  on request with coordination and computational
  semantics by worklets
• Ideal environment for integration with jacket
  micro-workflow

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Survivor NG Ideas

• Need widely distributed workflow repository
• Both definition and in-process state
• Cougaar-based implementation relies on a
  distributed blackboard/tuple space
• Any task processor may be enabled to acquire any
  part of the overall process
• Configurable Cougaar communities
• Worklets add dynamism, re-configurability,
  mobility to Cougaar communities
• To handle contingencies and overcome faults
• Need to add explicit fault-tolerance and security
  policies to Workflakes enactment mechanisms

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Next Steps

• Thats what were here to discuss

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