Elements of Web Services Choreography

1. Elements of Web Services Choreography Jean-Jacques Dubray WS-CHOR f2f 3/13/03 Redwood Shores, CA

2. Bio • Got interested by B2B, BPM and XML in 1998 at NEC System Laboratories • 1999 - eXcelon to develop a B2B Integration Server based on a Business Process Engine • 2001 - Eigner (PLM vendor) to design next generation architecture • Contributor to OAG (IF), ebXML (BPSS), and BPML (ebXML binding) • Represent no particular interest, just want to learn, share ideas and experiences

3. Outline • Introduction • Paradigm Shifts • WS-Choreography and SOA • Collaboration, Choreography and Orchestration • Elements of WS-Choreography • Message Exchange Patterns • Choreography protocol • Transactional behavior • Message content • Control flow • Technical Binding • Conclusions

4. Introduction • XML, Web Service and BPM will revolutionize the way we built applications • Applications as we know it will disappear • 1990-1999 looking for a better way to build applications (CORBA/DCOM, J2EE, but also EDOC, BOCA, …) • 2000-2010 found the better way • Towards a new “component model”: SOA

5. Paradigm Shifts • Can the web do for applications what it had done for humans? • From a given application access any service (data, transaction, computation) regardless of its location • Can the web give us hints on a better application model? • Loosely coupled, plug & play, Message based • REST? • Meta, Meta, Meta • Current programming languages show lots of limitations when developing business applications (e.g Java/J2EE, C#/.NET)

6. WS-Choreography is at the convergence of • B2B • EAI • Distributed computing model • Applications models (s.a. J2ee and .NET)

7. This is the WRONG Picture for SOA WS-Choreography and SOA Web Services Provider Web Services Provider Request Internet Response J2EE™ AppServer SOAP Messages .NET

8. What is a Service? This is A Service OAGIS 8.0 Scenario 41

9. SOA’s Foundation is “Peer-to-Peer” No Application Or Corporation Boundaries OAGIS 8.x Scenario 50

10. Intra / Inter CompanyMessage Exchange • Message exchange between corporation boundaries is sufficiently different to justify special treatments: • State alignment (no shared “memory”) • Legal aspects (non-repudiation)

11. SOA as an Application Model (MVC Revisited) Thin Fat Other Process & Data Federation Firewall Task Engine Process Engine ERP Model PLM1 Model PLM2 Model

12. Key Takeaway • Ws-chor is a major enabler of SOA • Ws-chor foundation is peer-to-peer

13. Collaboration, Executable Business Processes and Services ROLE Executable Business Process B2B Collaboration Message Exchange

14. Collaboration And Executable Business Process • Both are state machine • A collaboration has no engine associated with it (nothing is in the middle) • It is merely the execution of activities of the executable business processes in each party that advances the state of the collaboration

15. Collaboration And Executable Business Processes • The Process Engine is responsible for: • Mapping (many-to-one-one-to-many) • Decoupling services via message routing • sequence, flow, switch, while • Monitoring (coupled) interaction between services to advance the state of the process instance • A Collaboration “service” is responsible for ensuring that an incoming/outgoing message is expected at this point in time • No mapping, no routing, no “advancement”

16. Orchestration (Business) Components a.k.a. Services Review PO Task Map Route Process PO Process Sales Order

17. Choreography and Orchestration • Business component can exhibit a long running behavior and looking from the perspective of such component, the flow of messages between itself and other components can also be expressed using a meta language. • This is orchestration • The confusion is that Components are typically very coarse and can directly be exposed to partners. The long-running behavior might also be complete.

18. Choreography and Orchestration Failure Success

19. Key Takeaway • ws-chor applies to Collaboration and executable business processes • Orchestration might be different

20. Elements of WS-Choreography • What do we choreograph, how? • What is a message content? • Choreography between who/what? • Choreography technical binding

21. Choreograph Messages or Message Exchange Patterns? One way Notification Solicit Response Request Response

22. Message Exchange Pattern Choreography This is far easier than trying to choreograph Notifications and One ways Buyer Seller PO AckPO Change PO Change PO AckPO AckPO Invoice Payment

23. Choreography Protocol • There is a need, specially in B2B scenario to exchange signals in addition to messages • Signals feature typically a fixed format and carry special meaning • Message structure and content is valid • Message was successfully processed by the receiving application • Signals are typically part of the Message Exchange Pattern • Exception associated to signal content: business, technical exception

24. Choreograph Exceptions Buyer Supplier (Self) Order Entry Billing [TechnicalFailure] PO BTA1 PO [BusinessFailure] OpA1 Invoice [AnyFailure] OpA2 Invoice [AnyFailure] BTA2 [Success] Failure Success

25. Transactional Behavior • WSCI, BPEL4WS features transaction specifications as part of the choreography • BPEL4WS scopes • BPSS doesn’t, all compensating transactions must be explicit • Transactional behavior sounds reasonable to be within the scope of WS-Chor • First step is expressing meaningful exceptions: timeout, technical, business,…

26. Message Content • Any number of XML or Binary documents • XML document type or content might be used to specify condition expressions in the control flow

27. Control Flow Specification • Prof. van der Aalst patterns • BPEL4WS • WSCI • BPSS • Receive / Reply issue • BPML spawns a new sub process altogether • BPSS has an onInitiation condition • BPEL correlates a reply with a receive. The reply can be located anywhere in the choreography • Should consolidate to one control flow, no need for half-baked overlapping specification there.

28. Control Flow Specification Collaboration Control Flow Semantics are different from the semantics of an executable business process

29. Technical Binding • Two approaches • Start with WSDL specification and express a choreography of these services • I suggest an alternative approach which I think will work better • Specify the choreography in terms of roles and usage of message exchange pattern types • Then generate the corresponding WSDL automatically

30. Beyond Choreography • UMM • Business Collaboration Patterns & Monitored Commitments, e.g. from COOL: • Negotiation: Offer and Counter-offer • Offer and Acceptance • Commitment and Fulfillment • Deliver the goods and Pay for them • REA • http://homepage.interaccess.com/~linkage/REA4SCM.htm • Business Entities • http://www.collaborativedomain.com/standards/

31. Conclusion • SOA appears as a valid application model moving forward • No more application or corporation boundary • Process and Data federation • Decoupled services? • SOA is at the convergence of traditional application models, EAI and B2B • Service Choreography is essential to SOA

32. Conclusion • Service Choreography MUST be peer-to-peer • Scope is everything that is pure message exchange: Collaboration and EBP • Message Exchange Patterns are the units of what is being choreographed • B2B is different than EAI / Business Process Execution • More metadata is good by beware of metadata hell and poorly articulated layers