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

Bio Got interested by B2B, BPM and XML in 1998 at NEC System Laboratories eXcelon to develop a B2B Integration Server based on a Business Process Engine 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

Outline Introduction 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

Introduction XML, Web Service and BPM will revolutionize the way we built applications Applications as we know it will disappear – looking for a better way to build applications (CORBA/DCOM, J2EE, but also EDOC, BOCA, …) – found the better way Towards a new component model: SOA

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)

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

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

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

SOAs Foundation is Peer-to-Peer OAGIS 8.x Scenario 50 No Application Or Corporation Boundaries

Intra / Inter Company Message Exchange Message exchange between corporation boundaries is sufficiently different to justify special treatments: –State alignment (no shared memory) –Legal aspects (non-repudiation)

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

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

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

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

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

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

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.

Choreography and Orchestration SuccessFailure

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

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

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

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

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

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

Transactional Behavior WSCI, BPEL4WS features transaction specifications as part of the choreography –BPEL4WS scopes BPSS doesnt, 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,…

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

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.

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

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

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 – Business Entities –

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

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