Stages to Services (1) Web processes perform work  Here a CGI script controls programs which analyse bibliographic data in a PDF document

Stages to Services (2) Results returned in XML  Instead of returning flat text, structured XML results are displayed in the output frame.

Stages to Services (3) Results re-used in new ways  Search engine queries can be shown in a WAP environment, as a KWIC list or as page thumbnails. If only search engines returned XML…

Pre-Web Services Web server sends a document to a user

Post-Web Services Web server sends data to a program invoice item name price ref name price number=1 number=2 type = info id = xyz

Requirements for Services We need common transfer formats  SOAP We need to know how to contact the service  WDSL We need to know who offers services  UDDI

Web Service A translation service is advertised

SOAP Exposed How the request and response are constructed What’s German for “legality” ?

Using SOAP Construction of SOAP messages is automatic Call call = new Call(); call.setTargetObjectURI("urn:demo1:exchange"); call.setMethodName("getRate"); Vector params = new Vector(); params.addElement( new Parameter("country1", String.class, "USA", null )); params.addElement( new Parameter( "country2", String.class, "japan", null )); call.setParams( params ); Response response = call.invoke(" "" ); Using APACHE SOAP / see IBM Web Services (R)evolution Tutorial

Connecting to a Service The client can invoke  A local service (with no knowledge)  A Web Service (with currency expertise)

Making A Service Most hard work is achieved by reflection public class Exchange { public float getRate( String country1, String country2 ) { return F; }

Automation In previous example, client was constructed  By hand  From a human-readable web page We require a way of describing the service which is machine readable

WSDL Web Services Description Language  Similar to IDL  describes methods, parameters and results  allows both SOAP and raw HTTP comms

WSDL Automation WSDL descriptions can be derived automatically from source code  e.g. IBM WSTK or Microsoft.NET Development environment may automatically wrap as service, produce UI and manage service collectionmanage service collection  e.g. Microsoft.NET

WS Advantages Interoperability  Platform  Language  Development environment Ubiquity  HTTP / XML Low barrier to takeup Industry Support

WS Disadvantages Not there yet!  SOAP is fairly mature, allowing explicit RPC Apache / Jakarta  WSDL allows automatic generation of SOAP interfaces Microsoft.NET IBM WSTK

Statuses SOAP (v1.2) is a W3C Working Draft WSDL is a W3C Note UDDI is an Industry Initiative

Conclusion Web Services are a significant focus for Web community Development is ongoing Obvious step for E-commerce