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Chapter 12: Coordination Frameworks for Web Services

Chapter 12: Coordination Frameworks for Web Services. Service-Oriented Computing: Semantics, Processes, Agents – Munindar P. Singh and Michael N. Huhns, Wiley, 2005. Highlights of this Chapter. WSCL: Web Services Conversation Language WSCI: Web Service Choreography Interface WS-Coordination

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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. A Process Is … [Abstractions] Orchestration: A partial order of actions (activity graph, script) under the control of a central conductor; akin to a workflow [Global view; central] Workflow: narrower concept than process; emphasizes control and data flows from a central perspective; usually tool-specific and focused on human tasks Choreography: An exchange of messages among participants; akin to a conversation as described by WSCL, WS-CDL, ebBP [Global view; distributed] Collaboration: A joint set of activities among business partners [Local views; distributed] 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; the airline makes commits; the museum does not care 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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