Presented by: Francisco Martin-Recuerda

1. Web Services Coordination Framework WS-CFhttp://developers.sun.com/techtopics/webservices/wscaf/wscf.pdf Presented by: Francisco Martin-Recuerda

2. Overview • Introduction • Architecture • WS-CF Coordination Protocols • Open Issues

3. 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.

4. Introduction (II) WS-CF Web Services Stack

5. 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

6. 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).

7. 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.

8. 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.

9. 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).

10. Open Issues • Guarantee security and confidentiality. • Audit trail (log of actions). • Protocol completeness guarantee. • Quality of Service.