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Understanding Web Services Essentials

Learn the fundamentals of web services, including encapsulation, loose coupling, standard protocols like SOAP and WSDL, and how to invoke services using XML-RPC and SOAP messaging. Discover the self-describing and easily discoverable nature of web services.

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Understanding Web Services Essentials

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  1. CP3024 Lecture 10 Web Services

  2. What are Web Services? • “encapsulated, loosely coupled, contracted software objects offered via standard protocols” ZapThink Research

  3. Web Services • Encapsulated • Web Service implementation is invisible to entities outside the service • Exposes an interface but hides details • Loosely Coupled • Service and consumer software can be redesigned independently

  4. Web Services • Contracted • Description of service is available to consumer • Standard Protocols • TCP/IP • HTTP • XML • SOAP • WSDL • UDDI

  5. Self-describing • Every web service has a published public interface • Minimum of human readable documentation • SOAP services should have interfaces written in XML

  6. Discoverable • Simple mechanism for publishing details about a web service • Simple mechanism for finding a service and its interface • Mechanism could be completely decentralised or centralised registry

  7. A Web Service .. • Is available over network • Uses standardised XML messaging • Is independent of any given OS or language • Is self describing via XML • Is easily discoverable

  8. Web Usage Shift • Human-centric Web • Majority of web transactions initiated by a human • Application-centric Web • Inter-application interchanges • E.g. credit card approval

  9. A Web Service In Action XML XML

  10. Possible Protocols • HTTP POST/GET • XML-RPC • SOAP • Simple Object Access Protocol

  11. Example Service • Return a set of keys given a set of functional dependencies • Service called keyservice • Method called getCandidateKeys • String argument fdSet • Argument sent “{{a}->{b}}”

  12. XML-RPC Service Invocation <?xml version="1.0" encoding="ISO-8859-1"?> <methodCall> <methodName> keyservice.getCandidateKeys </methodName> <params> <param> <value>{{a}-&gt;{b}}</value> </param> </params> </methodCall>

  13. XML-RPC Response <?xml version="1.0" encoding="ISO-8859-1"?> <methodResponse> <params> <param> <value> {{a}} </value> </param> </params> </methodResponse>

  14. SOAP • SOAP envelope specification • Rules for encapsulating the data being transferred • Data encoding rules • Rules for encoding data types • RPC conventions • Rules for invoking remote methods

  15. Example Service Request <?xml version='1.0' encoding='UTF-8'?> <SOAP-ENV:Envelope xmlns:SOAP-ENV= http://schemas.xmlsoap.org/soap/envelope/ xmlns:xsi= "http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <SOAP-ENV:Body> <ns1:getCandidateKeys xmlns:ns1="urn:examples:keyservice" SOAP-ENV:encodingStyle= "http://schemas.xmlsoap.org/soap/encoding/"> <fdSet xsi:type="xsd:string">{{a}-&gt;{b}}</fdSet> </ns1:getCandidateKeys> </SOAP-ENV:Body> </SOAP-ENV:Envelope>

  16. Example Service Reply <?xml version='1.0' encoding='UTF-8'?> <SOAP-ENV:Envelope xmlns:SOAP-ENV= "http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsi= "http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <SOAP-ENV:Body> <ns1:getCandidateKeysResponse xmlns:ns1="urn:examples:keyservice" SOAP-ENV:encodingStyle= "http://schemas.xmlsoap.org/soap/encoding/"> <return xsi:type="xsd:string">{{a}}</return> </ns1:getCandidateKeysResponse> </SOAP-ENV:Body> </SOAP-ENV:Envelope>

  17. Soap Message Envelope (required) Header (optional) Body (required) Fault (optional) Structure of SOAP Messages

  18. Fault Response <?xml version='1.0' encoding='UTF-8'?> <SOAP-ENV:Envelope xmlns:SOAP-ENV= "http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsi= "http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <SOAP-ENV:Body> <SOAP-ENV:Fault> <faultcode>SOAP-ENV:Server</faultcode> <faultstring>Exception from service object: FD: Unexpected end of input</faultstring> <faultactor>/soap/servlet/rpcrouter</faultactor> </SOAP-ENV:Fault> </SOAP-ENV:Body> </SOAP-ENV:Envelope>

  19. Web Services Definition Language (WSDL) • Uses XML to describe a web service • Describes the interface of available functions • Specifies data type information for all requests and responses • Holds binding information about the transport protocol • Contains address information to locate the service

  20. Major Elements • definitions • types • message • portType • binding • ports • service

  21. WSDL definitions <definitions name="KeyService" targetNamespace= "http://localhost:8080/wsdl/Lucchesi.wsdl" xmlns="http://schemas.xmlsoap.org/wsdl/" xmlns:soap= "http://schemas.xmlsoap.org/wsdl/soap/" xmlns:tns= "http://localhost:8080/wsdl/Lucchesi.wsdl" xmlns:xsd="http://www.w3.org/2001/XMLSchema">

  22. WSDL types • Optional element • Defines complex types e.g. arrays and structures • Not used in the example

  23. WSDL message <message name="CandidateKeyRequest"> <part name="FDSet" type="xsd:string"/> </message> <message name="getKeys"> <part name="return" type="xsd:string"/> </message>

  24. WSDL portType <portType name="Key_PortType"> <operation name="getCandidateKeys"> <input message="tns:CandidateKeyRequest" name="Request"/> <output message="tns:getKeys“ name="Response"/> </operation> </portType>

  25. WSDL binding <binding name="Key_Binding" type="tns:Key_PortType"> <soap:binding style="rpc" transport="http://schemas.xmlsoap.org/soap/http"/> <operation name="getCandidateKeys"> <soap:operation soapAction="Generate keys"/> <input name="Request"> <soap:body encodingStyle= http://schemas.xmlsoap.org/soap/encoding/ namespace="urn:examples:keyservice" use="encoded"/> </input>

  26. WSDL Binding <output> <soap:body encodingStyle= "http://schemas.xmlsoap.org/soap/encoding/" namespace="urn:examples:keyservice" use="encoded"/> </output> </operation> </binding>

  27. WSDL Service <service name="Key_Service"> <documentation> WSDL File for KeyService </documentation> <port binding="tns:Key_Binding" name="Key_Port"> <soap:address location= “http://localhost:8080/soap/servlet/rpcrouter” /> </port> </service>

  28. WSDL In Action • Can use WSDL description to generate client code • Can use WSDL description to automatically invoke a service • Can generate WSDL from server code

  29. Available WSDL Services

  30. Generic Soap Client

  31. UDDI • Universal Description, Discovery and Integration • Specification for distributed directory of businesses • Data stored in an XML format • UDDI business registry • Launched May 2001 by IBM and Microsoft

  32. UDDI Development • Developed by IBM, Microsoft and Ariba • Ariba/IBM collaboration on B2B • IBM/Microsoft collaboration on SOAP • Microsoft/Ariba collaboration on BizTalk and cXML • Three revisions and then transfer to standards body • Launched September 2000

  33. UDDI Development • Version 2.0 announced July 2001 • Internationalisation • Complex organisations • Better searching mechanisms • Version 3.0 announced July 2002 • Increased security • Improved WSDL support • Multi-registry topologies • Proactive notifications

  34. UDDI Technical Architecture • UDDI data model • XML schema describing businesses and web services • UDDI API • SOAP based API for publishing and searching UDDI data • UDDI cloud services • Sites implementing UDDI which synchronise regularly

  35. UDDI Data Model • businessEntity • Information about a business • businessService • Information about a web service • bindingTemplate • Information about accessing a service • tModel • Pointer to external technical specification

  36. businessEntity businessService bindingTemplate tModel Relationships

  37. find_binding find_business find_service find_tModel get_bindingDetail get_businessDetail get_serviceDetail get_tModelDetail UDDI Inquiry API

  38. get_authToken discard_authToken save_binding save_business save_service save_tModel delete_binding delete_business delete_service delete_tModel UDDI Publishing API

  39. Use Of UDDI • Publishing • Advertise services • Allow discovery of standards in use • Searching • Locate details about electronic services of business partners • Search for suppliers

  40. Summary • Web Services • Mechanism for electronic business on the Web • Based on XML • SOAP • WSDL • UDDI

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