Web Services Orchestration and Choreography

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Web ServicesOrchestration and Choreography

• Presenter Min Lu
• Paper by Chris Peltz
• Nov 15, 2004

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Introduction

• Higher level, cross-organizational business
  process
• Two aspects of creating business process from
  composite web services.
• Orchestration one party
• Choreography multiple parties

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Topics of Discussion

• Process Design Requirements
• Emerging Standards
• BPEL
• WSCI
• BPML
• Case Study on BPEL
• Class Discussion
• My Conclusion

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Process Design Requirements

• Correlation
• Exception management transaction integrity
• Dynamic, flexibility and adaptability
• Recursive composition

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Process Design Requirements

• Correlation
• The ability to invoke services concurrently is an
  important requirement, especially when dealing
  with Asynchronous Web Services.
• Correlation identifiers

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Process Design Requirements

• Correlation
• Exception management transaction integrity
• Dynamic, flexibility and adaptability
• Recursive composition

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Process Design Requirements

• Exception management transaction integrity
• Web services that are long-running must be able
  to handle errors and time-out constraints
• Compensation transactions can undo an action

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Process Design Requirements

• Correlation
• Exception management transaction integrity
• Dynamic, flexibility and adaptability
• Recursive composition

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Process Design Requirements

• Dynamic, flexibility and adaptability
• Flexibility can be achieved by providing a clear
  separation between the process logic and the Web
  services invoked.
• An orchestration engine can achieve this
  separation.

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Process Design Requirements

• Correlation
• Exception management transaction integrity
• Dynamic, flexibility and adaptability
• Recursive composition

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Process Design Requirements

• Recursive composition
• Exposing processes through their own web service
  interfaces.

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Emerging Standards
Recent History of Business Process Standards
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Business Process Execution Language

• Support both executable abstract business
  processes.
• Executable process
• Specific interaction
• Models Orchestration
• Abstract process
• Message exchanges between parties
• Models Choreography

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Business Process Execution Language

• Support basic activity structured activity.
• Basic activity
• Interact external to the process itself
• Receive, invoke, respond
• Structured activity
• Manage the overall process flow
• Sequence, loop, dynamic branching

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BPEL4WS Process Flow
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Web Service Choreography Interface

• Defines choreography only
• Supports message correlation
• Supports exception handling
• Supports transaction integrity by transactional
  contexts
• Supports dynamic collaboration

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Web Service Choreography Interface

• Supports basic activities
• - Action tag defines requests response
• - Call tag invokes external services
• Supports structured activities
• - loop, sequence, parallel, etc.

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Web Service Choreography Interface

• WSCI only observe abstract process
• between web services

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Relationships
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Case Study Model
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Case Study on BPEL

• Defines partners and their roles
• ltpartnerLinksgt
• ltpartnerLink name"Buyer"
• partnerLinkType"porequestQuoteLinkType"
• myRole"Purchaser" partnerRole"Requestor"/gt
• ltpartnerLink name"Supplier1"
• partnerLinkType"porequestQuoteLinkType"
• myRole"Requestor" partnerRole"Purchaser"/gt
• lt!Set up other suppliers used in this process gt
• lt/partnerLinksgt

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Case Study on BPEL

• Defines variables
• ltvariablesgt
• ltvariable name"request"
• messageType"porequest"/gt
• ltvariable name"part_request
• messageType"popart_request"/gt
• ltvariable name"part_quote"
• messageType"popart_quote"/gt
• ltvariable name"proposal"
• messageType"poproposal"/gt
• lt/variablesgt

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Correlation of BPEL

• Correlate the requests by assign a unique quote
  and proposal identifier
• ltcorrelationSetsgt
• ltcorrelationSet name"Quote"
• properties"corquoteID"/gt
• ltcorrelationSet name"Proposal"
• properties"corproposalID"/gt
• lt/correlationSetsgt

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BPEL Basic Structured Activities

• ltsequencegt
• ltreceive name"receive" partnerLink"Buyer"
  operation"request" variable"request"
  initiate"yes"gt
• lt/receivegt
• ltflow name"supplier_flow"gt
• ltinvoke name"quote_supplier1" partnerLink"Suppli
  er1"
• operation"request_quote" inputVariable"part_req
  uest"
• outputVariable"part_quote"gt
• lt/invokegt
• lt!invoke other suppliers as part of the
  processgt
• lt/flowgt
• ltreply name"reply" partnerLink"Buyer"
• operation"send_proposal variable"proposal"gt
• lt/replygt
• lt/sequencegt

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Exception handling of BPEL

• If error occurs in contacting a supplier, the
  agent sends a message to the buyer.
• ltfaultHandlersgt
• ltcatch faultName"cantFulfillRequest"gt
• ltinvoke partnerLink"buyer"
• operation"sendError"
• inputVariable"fault"/gt
• lt/catchgt
• lt/faultHandlersgt

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Transaction Integrity of BPEL

• Compensation handlers
• E.g. if the agent cannot contact a supplier, the
  process must offer a way to roll back the order.

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Class Discussion

• Which process design requirements does BPEL meet?
  How?

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My Conclusion

• Correlation
• Assign unique identifiers and use
  ltcorrelationSetgt
• Supports asynchronous calls by declaring
  partnerLinkTypes to define what port types are
  used to send and/or receive messages on
• Exception handling Fault handler catch exception
• Transaction Integrity use ltscopegt for
  compensation transactions use
• Flexibility orchestration engine(IBM alpha
  Works, Collaxa)
• Recursive Composition see next question

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Class Discussion

• Does BPEL support recursive Web service
  composition?

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BPEL Recursive Composition

• Through the use of WSDL to denote the public
  interface
• BPEL orchestrates multiple Web services into a
  Web service, published by WSDL
• Subsequently can be orchestrated into another
  BPEL
• External. Done through the public interface