Service-Oriented Computing: Semantics, Processes, Agents August 2004 Chapter 12: Coordination Frameworks for Web Services Service-Oriented Computing: Semantics, Processes, Agents – Munindar P. Singh and Michael N. Huhns, Wiley, 2005 © Singh & Huhns

Highlights of this Chapter Service-Oriented Computing: Semantics, Processes, Agents August 2004 Highlights of this Chapter WSCL: Web Services Conversation Language WSCI: Web Service Choreography Interface WS-Coordination Web service transaction types BTP: Business Transaction Protocol Chapter 12 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns © Singh & Huhns

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!) Chapter 12 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

A Process Is … [Abstractions] Service-Oriented Computing: Semantics, Processes, Agents August 2004 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] Chapter 13 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns © Singh & Huhns

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> <DestinationInteraction href="CatalogInquiry"/> Conversation: a name for the protocol and a list of its interactions and transitions; this is one party’s perspective Chapter 12 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

Concepts in WSCL Chapter 12                                                                                                                                                 Concepts in WSCL Chapter 12 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

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 Chapter 12 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

Example Conversation Definition Chapter 12 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

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> Chapter 12 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

Example WSCL Specification: 2 <ConversationTransitions> <Transition> <SourceInteraction href="Start"/> <DestinationInteraction href="Login"/> </Transition> … <SourceInteraction href="Login"/> <DestinationInteraction href="Registration"/> <SourceInteractionCondition href="InvalidLoginRS"/> <SourceInteraction href="Logout"/> <DestinationInteraction href="End"/> </ConversationTransitions> </Conversation> Chapter 12 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

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) Chapter 12 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

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"/> </interface> Chapter 12 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

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> Chapter 12 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

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 Chapter 12 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

WS-Coordination Service Chapter 12 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

WS-Coordination Service Chapter 12 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

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 Chapter 12 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

Business Transaction Protocol (BTP) Chapter 12 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

Service-Oriented Computing: Semantics, Processes, Agents August 2004 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 Chapter 12 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns © Singh & Huhns