Task Model for Process Composition

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Task Model for Process Composition

• Stuart Wheater
• Santosh Shrivastava

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Objective

• Distributed applications constructed by combining
  existing applications
• Such applications can be very complex in
  structure
• Contain many notification and dataflow
  dependencies between their constituent
  applications
• The execution of such an application may take a
  long time to complete, and may contain long
  periods of inactivity
• Long running applications will require support
  for fault-tolerance machines may fail, services
  may be moved or withdrawn

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Computational Model

• Computational model for expressing process logic
• Tasks
• Dependencies
• Task composition

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Tasks

• Can have multiple input sets
• Contains a set of input objects
• The first complete input set causes a task to be
  started
• Can have multiple output sets
• Contains a set of output objects
• A task can produces one output set

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Dependencies Types
Sink
Notification Dependencies
Source Output
Source Input
Input
Output
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Example of Tasks and Dependences
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Compound Tasks

• Compositional building blocks for collections of
  tasks
• The first complete output set causes a compound
  task to be completed

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Genesis Tasks

• Tasks which instantiate a workflow definition
  when executed
• Allows just in time instantiation
• Allows recursive execution of defined workflows

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Model Summary

• Tasks
• Multiple ways of starting (input sets)
• Multiple ways of completing (output sets)
• Recursive task definition
• Compound tasks
• Recursive task execution
• Genesis task
• Multiple input sources
• Redundant sources of input

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Flexible Task Composition

• Application level fault-tolerance
• Alternative tasks
• Compensating tasks
• Forward error recovery
• Backward error recovery
• Input time-out support tasks

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Alternative Tasks

• Primary task A
• Alternative task A
• If A fails A is started
• With same input
• B will be triggered by successful completion of A
  or A
• Otherwise another process could be triggered

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Compensating Tasks

• Task C outcomes
• Successful
• Nothing
• Partial
• Forward error recovery
• Backward error recovery

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Input Time-Out Support Tasks

• If task E does not complete within required time,
  task TO will trigger task F using secondary input
  set.

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Process Deployment Model
Deployment definition
Processdefinition

• Process definition contains annotations which are
  interpreted based on the deployment definition

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Process Deployment Definition
Organisation
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Process Deployment Definition
Provided Processes
Organisation
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Process Deployment Definition
Required Processes
Organisation
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Example Deployment
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Summary

• Computational Model
• Deployment Model

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