Support%20for%20Automatic%20Workflow%20Composition%20in%20Semantic%20Grid%20Environemnt

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Support for Automatic Workflow Composition in
Semantic Grid Environemnt

• Tomasz Gubala, Marian Bubak, Maciej Malawski
• Institute of Computer Science and Cyfronet,
• AGH University of Science and Technology,
• Kraków, Poland

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Grid Workflows

• Grid workflows
• Provide a method to (de)compose applications
• Naturally support parallel computations
• Allow to program grid through specifying
  inter-component dependencies
• Multiple levels of abstraction in workflows
• Separate execution details from application logic
• Allow for workflow reusability (the application
  is able to overcome Grid dynamic nature)
• Ease the application execution process as the
  user does not has to learn all the
  midleware-specific details

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Motivation

• Motivation (Grid Invisibility)
• It is sometimes not trivial to compose a new
  application manually (even using nice graph-based
  widgets)
• Users not always realize the actual needs
  (requirements) of a certain computation
• It is difficult task to choose (using a browser)
  among hundreds of grid resources dispersed
  worldwide
• Use scenario
• Specify what you need as a result choosing a
  concept
• Machine builds several possible solutions as
  workflow
• Choose one with an aid of a user assistant tool

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Solution Step 1

• The user wants a meteo application execution
• The application is supposed to provide weather
  prediction data
• The user chooses WeatherData concept using User
  Assistant Agent
• The basic workflow skeleton (see right) is
  generated

Begin
GridJob
WeatherData
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Solution Step 2

• The tool identifies a single data dependency
• It contacts a registry to find a class of
  services being capable of delivering WeatherData
• Newly found building block is inserted into the
  workflow, but...
• ...it generates new dependencies

MM5Boundary Conditions
Topological DataUploaded
MM5.calc
WeatherData
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Solution Step 3

• Using follow-up technique the tool constructs the
  entire workflow step-by-step
• Support for both control and data flow constructs
• Several patterns supported
• XOR-merge
• AND-merge
• AND-split
• loop

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Result

• As a result the newly created workflow
• supports parallel execution,
• is a valid PetriNet workflow in a specified
  language,
• is abstract and non-executable,
• the tool operates on abstract notion of service
  class operations
• it needs a specific mapper, another tool that
  concretizes it
• may be reused many times,
• as there may be many different instances of
  certain type of service
• still includes some red parts where a user has to
  supply important data.

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Semantic Service Discovery

• IOPE technique
• IOPE (input, output, precondition, effect)
• Every data request sets several constraints
• Usually they constrain content, format and
  storing mechanism
• Every service operation defines its input and
  output parameters as data templates
• With similar constraints on content, format and
  storage place

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Templates and Instances

• Data template
• Describes an abstract class of data (all the data
  that fits)
• Data instance
• Metadata description of real piece of data stored
  somewhere

What is the meaning of data content
Data Template
Data Instance
content constraint
contains
What is the format the data has
format constraint
has format
Where is the data stored
storage constraint
is stored in
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Comparison

• Comparison guidelines
• A certain operation output fits perfectly if it
  produces a data template with equal or more
  restrictive constraints then needed
• Inexact match
• When fits, but
• is different (we need an additional
  transformation activity in between), and/or
• is different (we need an additional
  relocation activity in between)
• Transformation/relocation
• generic operation changing format or storage
  properties of data and not concerned about the
  content of the data
• E.g. .tex to .html converter or file-from-url
  retriever

content constraint
format constraint
storage constraint
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Current State, Future Work

• First prototype of the workflow compositor to be
  finished this winter
• Stable release due to end of 2006
• Better matchmaking capabilities based on more
  sophisticated data/service descriptions
• Some more workflow patterns properly supported
• To be deployed as a standalone service (is just a
  .jar now)
• Possibility of employing semantic workflow
  comparison algorithms in order to reuse similar
  solution constructed so far

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• Thank you very much for your attention
• http//www.kwfgrid.net/
• http//www.gridworkflow.org/