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Chapter 12: Coordination Frameworks for Web Services

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This chapter explores the coordination frameworks critical for achieving business interoperation in service-oriented computing. Highlighted concepts include the Web Services Conversation Language (WSCL), Web Services Choreography Interface (WSCI), and the Business Transaction Protocol (BTP). Key agreements among parties encompass identity, transport protocols, document semantics, and business protocol expectations. The text defines orchestration, choreography, and collaboration, offering insights into workflow processes and WSCL specifications, including interaction types and conversation definitions essential for well-formed service interactions.

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Chapter 12: Coordination Frameworks for Web Services

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  1. Chapter 12:Coordination Frameworks for Web Services Service-Oriented Computing: Semantics, Processes, Agents– Munindar P. Singh and Michael N. Huhns, Wiley, 2005

  2. Highlights of this Chapter • WSCL: Web Services Conversation Language • WSCI: Web Service Choreography Interface • WS-Coordination • Web service transaction types • BTP: Business Transaction Protocol Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  3. Achieving Business Interoperation The parties must • Know each other’s identity and location (presumes suitable directories) • Agree on the low-level transport protocols and encoding formats • Agree on the syntax and semantics of documents to be exchanged • Agree on their expectations about when different documents will be sent and received • This specification is termed a business protocol • An instance of a business protocol is a conversation (but sometimes the term is used to mean protocol – watch out!) Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  4. Process Abstractions Orchestration: A process is a partial order of actions under the control of a central conductor; akin to a workflow [Global; central] Choreography: A process is an exchange of messages among participants; akin to a conversation as described by WSCL and WSCI [Global; distributed] Collaboration: A process is a joint set of activities among business partners [Local; distributed] Workflow: narrower concept than process, which emphasizes control and data flows from a central perspective; original idea behind modern orchestration Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  5. Parts of a WSCL Specification WSCL: Web Services Conversation Language • Document Type Definitions: specify what types of XML documents will be exchanged • Interaction Types: Send, Receive, SendReceive, ReceiveSend, Empty <Interaction interactionType="SendReceive" id="Payment"> <OutboundXMLDocument id="Invoice" hrefSchema="http://sc.edu/InvoiceRS.xsd"/> <InboundXMLDocument id="Payment" hrefSchema="http://ncsu.edu/Payment.xsd"> </InboundXMLDocument> </Interaction> • Transitions: order of the interactions <Transition> <SourceInteraction href="Quote"/> <DestinationInteraction href="Purchase"/> </Transition> <Transition> <SourceInteraction href="Quote"/> <DestinationInteraction href="CatalogInquiry"/> </Transition> • Conversation: a name for the protocol and a list of its interactions and transitions; this is one party’s perspective Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  6. Concepts in WSCL Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  7. Well-Formed Conversations • All interactions are reachable from the initial interaction • The final interaction is reachable from all interactions • If a transition from interaction A to interaction B specifies a SourceInteractionCondition, then all transitions from A to B do so • The final interaction and transitions to the final interaction unambiguously clarify for each participant when a conversation is finished Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  8. Example Conversation Definition Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  9. Example WSCL Specification: 1 <Conversation name="StoreFrontServiceConversation" xmlns="http://www.w3.org/2002/02/wscl10" initialInteraction="Start" finalInteraction="End" > <ConversationInteractions> <Interaction interactionType="ReceiveSend" id="Login"> <InboundXMLDocument hrefSchema=“http://conv1.org/LoginRQ.xsd” id="LoginRQ"/> <OutboundXMLDocument hrefSchema=“http://conv1.org/ValidLoginRS.xsd” id="ValidLoginRS"/> <OutboundXMLDocument id="InvalidLoginRS" hrefSchema=“http://conv1.org/InvalidLoginRS.xsd”/> </Interaction> … <Interaction interactionType="Empty" id="Start" /> <Interaction interactionType="Empty" id="End" /> </ConversationInteractions> Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  10. Example WSCL Specification: 2 <ConversationTransitions> <Transition> <SourceInteraction href="Start"/> <DestinationInteraction href="Login"/> </Transition> … <Transition> <SourceInteraction href="Login"/> <DestinationInteraction href="Registration"/> <SourceInteractionCondition href="InvalidLoginRS"/> </Transition> <Transition> <SourceInteraction href="Logout"/> <DestinationInteraction href="End"/> </Transition> </ConversationTransitions> </Conversation> Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  11. WSCI: Web Service Choreography Interface Choreography refers to a global view of how messages are exchanged • WSCI describes the flow of messages exchanged by a Web service that is interacting with other services • WSCI is viewed as an enhancement to WSDL (inserted within a WSDL description) Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  12. Example WSCI Add-In to WSDL <correlation name="quotationCorrelation“ property="tns:quotationID“/> <interface name="StockQuoteWS"> <process name="ProvideStockQuote" instantiation="message"> <sequence> <action name="ReceiveLogin“ role="tns:StockQuoteWS“ operation="tns:QuoteToUser/LogIn"/> <action name="ReceiveStockQuoteRequest" role="tns:StockQuoteWS" operation="tns:QuoteToUser/ProvideQuote"> <correlate correlation="tns:quotationCorrelation"/> <call process="tns:LookupPrice"/> </action> <action name="ReceiveLogout“ role="tns:StockQuoteWS“ operation="tns:QuoteToUser/LogOut"/> </sequence> </process> <process name="LookupPrice" instantiation="other"> <action name="QueryNYSE" role="tns:StockQuoteWS“ operation="tns:QuoteToUser/QueryNYSE"/> </process> </interface> Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  13. WSCI Example for Transaction Compensation <sequence> <context> <transaction name="buyStock" type="atomic"> <compensation> <action name="NotifyUnavailable" role="NYSE“ operation="tns:NYSEtoBroker/NotifyUnavailable"/> </compensation> </transaction> </context> <action name="BuyShare" role ="Broker“ operation="tns:BrokerToNYSE/BuyShare"/> <while name="BuyShares"> <condition>defs:fundsRemain</condition> <action name="BuyShare" role ="Broker“ operation="tns:BrokerToNYSE/BuyShare"> <correlate correlation="defs:buyingCorrelation"/> </action> </while> </sequence> <!-- Compensating Behavior for the Above Transaction --> <exception> <onTimeout property="tns:expiryTime" type="duration" reference="tns:BuyShares@end"> <compensate transaction="tns:buyStock"/> </onTimeout> </exception> Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  14. WS-Coordination • WS-Coordination is the specification for a service whose job is to coordinate the activities of the Web services that are part of a business process • A coordination service is an aggregation of three services: • Registration: for parties to register with the coordinator • Activation: to create an instance of a coordination context • Coordination protocol: to define the specific protocol to be followed Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  15. WS-Coordination Service Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  16. WS-Coordination Service Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  17. WS-AtomicTransaction:Protocol for an Atomic Transaction The travel agency and the airline can perform 2PC, but the museum can perform only a simple, zero-phase update Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  18. Business Transaction Protocol (BTP) Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  19. Chapter 12 Summary • SOC needs an ability to specify interactions among business partners in a manner that respects the partners’ autonomy and heterogeneity: conversations are a natural way to do so • SOC needs support for transactions • The more relaxed varieties are preferable, but there is a place for traditional transactions as well • The transactions are based on a small set of primitives Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

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