Web Services Coordination Framework WS-CF http

							Web Services Coordination
      Framework
         WS-CF
http://developers.sun.com/techtopics/webservices/wscaf/wscf.pdf


        Presented by: Francisco Martin-Recuerda
                  Overview
• Introduction
• Architecture
• WS-CF Coordination Protocols
• Open Issues




                     Francisco Martin-Recuerda   2
                     Introduction
• WS-CF specifies a software agent to handle context
  management through coordinator.
• Coordination is necessary for distributed applications
  (i.e. Web Services in choreography)
• Defines a Web Service Coordinator:
   – Context Management.
   – Maintain a repository of participants.
   – Guarantee that the participants get the results of the
     coordinated interaction.
   – Uses SOAP to encode messages and WSDL to use a
     synchronous invocation style for sending requests.

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        Introduction (II)




WS-CF                             Web Services Stack

             Francisco Martin-Recuerda                 4
                          Architecture
• Web Service Coordinator:
   – Provides an interface for the registration of participants and activities.
   – Disseminates information to a number of participants and guarantees
     that all of them get the information.
   – Manages the context.
   – Context information can flow inside messages sent to the participants.
   – A coordinator can be also a participant to another coordinator,
     extending the ability to interoperate accross application domain.
• Participants:
   – cooperating Web Services in a composite unit of work
   – share a common context


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                    Architecture (II)
• Activity:
   – Represent a defined set of tasks with a set of related coordination
     actions.
   – Involved one or more elements (participants that interacts through a
     coordinated).
• Coordination Service:
   – Defines and provides a processing pattern (model).
   – Example: ACID transaction service provides a protocol that defines a
     sequence processing: Prepare, Commit and Rollback.
   – Also defines how activities are coordinated (activities can cooperate
     with each other).



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               Architecture (III)
• Protocol Configuration and Negotiation:
  – Defines a protocol negotiation between web services to
    determine which Coordination Service model will be used.
  – Determines which protocol message exchange will be
    used.
  – Defines a method to communicate the results of a
    process.
  – Defines the message interactions between the coordinator
    and its participants.
  – Unambiguously identied by a URI.


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 WS-CF Coordination Protocols
Coordinator to participant interactions
  – Messages can start the execution of a particular task
    for a specific participant or
  – Ask for the current state of the execution or
  – Return or distribute results of the execution of some
    process.
Service to coordinator interactions
  – Basically defines how a service can ask to a
    coordinator to register or unregister participants for
    an specific activity.

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 WS-CF Coordination Protocols
Client to coordinator
  – Basically defienes how a client (user) of the
    coordination service can obtain the status of the
    coordination or ask it to perform coordination.
Interposition
  – As we mentioned before, coordinator can be also
    participants for other coordinator.
  – Reduces overhead using proxy coordinator (or
    subordinate coordinators).

                        Francisco Martin-Recuerda       9
                   Open Issues
•   Guarantee security and confidentiality.
•   Audit trail (log of actions).
•   Protocol completeness guarantee.
•   Quality of Service.




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