CP3024 Lecture 10 Web Services

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

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

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

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

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

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

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

A Web Service In Action XML

Possible Protocols  HTTP POST/GET  XML-RPC  SOAP –Simple Object Access Protocol

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}}”

XML-RPC Service Invocation keyservice.getCandidateKeys {{a}->{b}}

XML-RPC Response {{a}}

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

Example Service Request <SOAP-ENV:Envelope xmlns:SOAP-ENV= xmlns:xsi= " xmlns:xsd=" <ns1:getCandidateKeys xmlns:ns1="urn:examples:keyservice" SOAP-ENV:encodingStyle= " {{a}->{b}}

Example Service Reply <SOAP-ENV:Envelope xmlns:SOAP-ENV= " xmlns:xsi= " xmlns:xsd=" <ns1:getCandidateKeysResponse xmlns:ns1="urn:examples:keyservice" SOAP-ENV:encodingStyle= " {{a}}

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

Fault Response <SOAP-ENV:Envelope xmlns:SOAP-ENV= " xmlns:xsi= " xmlns:xsd=" SOAP-ENV:Server Exception from service object: FD: Unexpected end of input /soap/servlet/rpcrouter

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

Major Elements  definitions –types –message –portType –binding –ports –service

WSDL definitions <definitions name="KeyService" targetNamespace= " xmlns=" xmlns:soap= " xmlns:tns= " xmlns:xsd="

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

WSDL message

WSDL portType <output message="tns:getKeys“ name="Response"/>

WSDL binding <soap:binding style="rpc" transport=" <soap:body encodingStyle= namespace="urn:examples:keyservice" use="encoded"/>

WSDL Binding <soap:body encodingStyle= " namespace="urn:examples:keyservice" use="encoded"/>

WSDL Service WSDL File for KeyService <soap:address location= “ />

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

Available WSDL Services

Generic Soap Client

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

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

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

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

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

businessService Relationships businessEntitybindingTemplatetModel

UDDI Inquiry API  find_binding  find_business  find_service  find_tModel  get_bindingDetail  get_businessDetail  get_serviceDetail  get_tModelDetail

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

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

Summary  Web Services –Mechanism for electronic business on the Web  Based on XML  SOAP  WSDL  UDDI