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

item

name

price

ref

name

price

number=1

number=2

type = info

id = xyz

Requirements for Services

We need common transfer formatsSOAP

We need to know how to contact the serviceWDSL

We need to know who offers servicesUDDI

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("http://xmethods.net/soap", "" );

Using APACHE SOAP / see IBM Web Services (R)evolution Tutorial

Connecting to a Service

The client can invokeA 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 144.52F;

}

}

Automation

In previous example, client was constructedBy handFrom a human-readable web page

We require a way of describing the service which is machine readable

WSDL

Web Services Description LanguageSimilar to IDLdescribes methods, parameters and resultsallows both SOAP and raw HTTP comms

WSDL Automation

WSDL descriptions can be derived automatically from source codee.g. IBM WSTK or Microsoft .NET

Development environment may automatically wrap as service, produce UI and manage service collectione.g. Microsoft .NET

WS Advantages

InteroperabilityPlatformLanguageDevelopment environment

UbiquityHTTP / 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