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

Chapter 122Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 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 123Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael 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 124Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 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

Chapter 125Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael 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 <OutboundXMLDocument id="Invoice" hrefSchema=" <InboundXMLDocument id="Payment" hrefSchema=" Transitions: order of the interactions Conversation: a name for the protocol and a list of its interactions and transitions; this is one party’s perspective

Chapter 126Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Concepts in WSCL

Chapter 127Service-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 128Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Example Conversation Definition

Chapter 129Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Example WSCL Specification: 1 <InboundXMLDocument hrefSchema=“ id="LoginRQ"/> <OutboundXMLDocument hrefSchema=“ id="ValidLoginRS"/> …

Chapter 1210Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Example WSCL Specification: 2 …

Chapter 1211Service-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 1212Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Example WSCI Add-In to WSDL <action name="ReceiveLogin“ role="tns:StockQuoteWS“ operation="tns:QuoteToUser/LogIn"/> <action name="ReceiveStockQuoteRequest" role="tns:StockQuoteWS" operation="tns:QuoteToUser/ProvideQuote"> <action name="ReceiveLogout“ role="tns:StockQuoteWS“ operation="tns:QuoteToUser/LogOut"/> <action name="QueryNYSE" role="tns:StockQuoteWS“ operation="tns:QuoteToUser/QueryNYSE"/>

Chapter 1213Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns WSCI Example for Transaction Compensation defs:fundsRemain

Chapter 1214Service-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 1215Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns WS-Coordination Service

Chapter 1216Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns WS-Coordination Service

Chapter 1217Service-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, but the museum can perform only a simple, zero-phase update

Chapter 1218Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Business Transaction Protocol (BTP)

Chapter 1219Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 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