Web Service Choreography Interface (Wsci)
- 1. Web Service Choreography Interface (WSCI) a.k.a. Whiskey!!!
- 2. Contributors Intalio Sun Microsystems SAP BEA
- 3. Definitions Orchestration – Deals with communication actions and internal actions in which a service engages. Not necessarily all contained in behavioral interfaces. Meant to be execute by an orchestration engine Choreography – Deals with collaboration between a collection of services in order to achieve goal. Captures interactions and their dependences to do so. Does not describe any internal action that occurs within a service that is not directly visible.
- 4. Orchestration Players WSFL from IBM XLANG from Microsoft BPEL4WS Which combined WSFL and XLANG Specifically execution processes BPML Uses WSCI to do it choreography! Also considered a superset of BPEL4WS
- 5. Choreography Players BPEL4WS Specifically abstract processes WSCI (Whiskey!)
- 6. Issues Already? There seems to be a lot of confusion between these terms. No consistent definition across domains. Most common separations: Orchestration – Involves business processes Choreography – Way that different methods are called with one another (semantics of message passing).
- 7. Introduction to WSCI Notion of static definition versus dynamic definition WSDL defines static definitions Atomic in nature Only describe direction of message but not behavior of service with each operation WSCI aims to provide a dynamic definition that can take into account boundaries beyond single operation (stateful)
- 8. Problems with just WSDL No message sequencing No start and end of a sequence of messages No undoing operations (transactional semantics) No global view of overall exchange?
- 9. WSCI Overview In order to solve these issues, WSCI supports stateful message exchange with Message Choreography – define bounds of message exchange and rules for ordering Transactional Semantics – bounds and compensating instructions Exception Handling – define how WS will react to exception Thread Management – how WS manages multiple conversations and required relationship among parts of different messages in same exchange Properties and Selectors – way of setting runtime values from WSCI perspective Connectors - describe actually linkage of different web services Context – Set context from which to have functions (local functions / variables in Java, etc.
- 11. Simple Example <correlation name = "itineraryCorrelation" property = "tns:itineraryID"> </correlation> <interface name = "TravelAgent"> <process name = "PlanAndBookTrip" instantiation = "message"> <sequence> <action name = "ReceiveTripOrder" role = "tns:TravelAgent" operation = "tns:TAtoTraveler/OrderTrip"> </action> <action name = "ReceiveConfirmation" role = "tns:TravelAgent" operation = "tns:TAtoTraveler/bookTickets"> <correlate correlation="tns:itineraryCorrelation"/> <call process = "tns:BookSeats" /> </action> <action name = "SendStatement" role = "tns:TravelAgent" operation = "tns:TAtoTraveler/SendStatement"/> </action> </sequence> </process> <process name = "BookSeats" instantiation = "other"> <action name = "bookSeats" role = "tns:TravelAgent" operation = "tns:TAtoAirline/bookSeats"> </action> </process> </interface>
- 12. WSCI Concepts – Activities WSCI describes behavior of a WS in terms of choreographed activities (2 types) Atomic Activity (1-1 WSDL Correspondence) (actions) Complex Activity (made up of atomic and complex activities) – types of Complex Activities: All – performs activities in any order Sequence – activities must be performed in a sequential order Choice – choose between activity set to perform (activity set) based on input On message – based on role, action and message On timeout On fault (much like try / catch) For-each, until and while – loop for some condition Switch – choose one activity set and do in sequential order Some others like fault (throw), delay, empty
- 13. WSCI Concepts – Properties / Correlations If activities are the methods of WSCI then properties are the variables Way of getting specific information out of an input method and store to some property (name / value combo). Able to extract information from XML message by using specific XPath query. Can be referenced anywhere within WSCI. Very important place this is used is in correlations. Correlations are special types of properties that are meant to make activites stateful. They correlate some transaction-indicating id between two activities.
- 14. WSCI Concepts - Context Much like how locality works with variables and functions in OO. A context has its own set of variables and methods including that of its parents (but not children) Transactional Ideas modeled in context (context declared as a transaction thus observe ACID properties).
- 15. WSCI Concepts - Processes Follows much of the logic of processes (threads) from OS concepts Process – A special type of activity that establishes its own context of execution Can be nested or top-level. Can also say if it can be called from Top-level or only nested. Process can create a new one by calling ( use call ) it (wait for child to finish) or spawn (run in parallel). Other method for receiving it is from a message (not from another process) Join – way of enforcing barriers (wait for instances of a process to finish before completing)
- 16. WSCI Concepts – Exception Handling Functions much like try/catch in java Can throw exceptions by using special action type fault Use choice w/ onFault to do try/catch block Event propagation follows like Java (parent handles if child can’t handle exception)
- 17. WSCI Concepts - Transactions Support for 2 types of transactions that can be declared in context Atomic Transaction – follow ACID properties in that all either do everything or nothing Open Transactions – weaker notion that has many atomic transactions in it but uses “compensating transactions” to rollback long chains
- 18. WSCI Concepts – Global Model Able to have oriented view of overall processes. Links indicate direct message flow between linked operations e.g. <model name = “airlineTicketing> <connect operatoins = “tra:TravelerToTA/PlaceItenerary ta:TAtoTraveler/ReceiveTrip” /> </model>
- 20. Questions? ?