CS 290C: Formal Models for Web Software Lectures 11 and 12: Formal Modeling and Verification of Web Services, Orchestration and ChoreographyInstructor: Tevfik BultanWeb Revolution Sharing information using Internet has been a big success Key components Internet Internet protocols such as TCP/IP WWW and HTTP HTML format Web browsers Sharing information using the http+html+browser framework has been successful in a lot of applications List your favorite web sites hereWhat Next? There are applications where http+html+browser framework does not work Business to business applications HTML is developed for displaying information in a way that is understandable for humans HTML is not very useful in helping computers understand the content Basic Question Can we extend the interaction and sharing that WWW created among humans to interaction and sharing among services where the services share information and collaborate using the Internet?More Questions What should be the format that the services share the information? How will the information format be defined? What protocol will the computers use to send and receive information? How can a computer find out about the information provided by another computer? How can we describe the interaction among multiple computers?Some Proposed Answers What should be the format that the services share the information? XML How will the information format be defined? XML Schema What protocol will the services use to send and receive information? SOAP How can a service find out about the information provided by another service? WSDL, UDDI How can we describe the interaction among multiple services? BPEL, WS-CDLWeb Services Standards StackDataTypeService Orchestration ProtocolWS-BPELWeb Service StandardsImplementation PlatformsMicrosoft .Net, Sun J2EEWSDL, UDDISOAPXML SchemaXMLWS-CDLChoreography What are Web Services? Web services can be described as web accessible software that provide interfaces for service description, discovery, and interactionWeb Services: Challenges Web services implemented using different implementation platforms should be able to interact with each other There are different implementation platforms such as .Net or J2EE It should be possible to modify an existing web service without modifying other services that interact with it Web services should be able tolerate pauses in availability of other services and slow data transmissionWeb Services: ChallengesCant we solve these challenges with existing technologies? Existing technologies for distributed computing such as CORBA and RMI require tight coupling among applications It is not possible to specify interactions among services using stateless protocolsWeb Services: CharacteristicsWeb services address these challenges with the following common characteristics: Standardized data transmission via XML Loose coupling among interacting web services through standardized interfaces Message based communicationWeb Services The World Wide Web Consortium (W3C) defines a Web service as “a software system designed to support interoperable machine-to-machine interaction over a network” The basic architectureService RequesterService ProviderService BrokerRegisterSearchRequestResponseWeb Services Standards StackDataTypeService RegistryProtocolUniversal Description, Discovery where ordered message exchanges result in accomplishing a common business goal. A WS-CDL specification describes the interaction ordering among a set of peers using basic and structured activities Basic activities: INTERACTION, PERFORM, ASSIGN, SILENT ACTION, NO ACTION Structured activities: SEQUENCE, PARALLEL, CHOICE, PICK, FLOW, SCOPE, COMPENSATEWeb Services Standards StackDataTypeService OrchestrationProtocolWeb Services Business Process Execution Language (WS-BPEL)Web Services Description Language (WSDL)Simple Object Access Protocol (SOAP)XML Schema (XSD)Extensible Markup Language (XML)Atomic ServiceAtomic ServiceOrchestrated ServiceSOAPWSDLWSDLChoreographyWeb Services Choreography Description Language (WS-CDL)WS-BPELOrchestrated ServiceWS-BPELSOAPSOAPSOAPSOAPWS-CDLAn Example: Stock Analysis ServiceThe stock analysis service involves: three peers Investor, Stock Broker Firm, and Research DepartmentHere is how the stock analysis service operates: Investor initiates the stock analysis service by sending a register message to the Stock Broker Firm The Stock Broker Firm may accept or reject the registration If the registration is accepted, the Stock Broker Firm sends an analysis request to the Research DepartmentAn Example: Stock Analysis Service Research Department sends the results of the analysis directly to the Investor as a report After receiving a report the Investor can either send an ack to the Stock Broker Firm or cancel the service Then, the Stock Broker Firm either sends the bill for the services to