Web Services :

Web Services makes best utilization of wide spreaded internet protocals.I the idea of web services is to provide the distributed computing in a distributed environment.Prier to web services CORBA from Object Management Group and COM/DCOM from Microsoft played a vital role for distributed computing.With CORBA and COM/DOCM there are technical problems especially while making a Remote Procedure Call from a remote client .If suppose the sever got some internal problems and could 't respond to its client then the RPC making client simply goes into infinite waiting sate.It is the system designer responsibility to deal these kind of problems with the traditional distributed computing.These kind of problems are no longer exist with the web services.

Web Services laid a foundation for Service Oriented Architecture,SOA.Using web services we can integrate any kind of applications irrespective of their languages,under laying operating systems and even hardware.

An application developed in .net environment can be integrated in to an application developed in J2EE environment .A C++/COBOL/Phyton/PHP web service can easily be integrated in to a J2EE application or vice versa using web servies.If you use Web service there will be no Obsolete code.

Depending on the way of operation we have SOAP/WSDL based Web Services and REpresentational State Transfer web services also known as RESTful web servies.RESTful is a new way of creating web services.

SOAP/WSDL based Web Services are in wide usage. JAX-RPC & JAX-WS are SOAP/WSDL based webservices.JAX-WS Web Services are very powerful compared to JAX-RPC Webservices.With JAX-WS web service has well defined mechanism for security concerns but JAX-RPC dos' t address security concerns and leaves it to the developer to handle the risks.

WSDL is the heart of the a web service.WSDL describes the web service.WSDL contains four important elements.

1 Port Type : Port type is the most important WSDL element.Port type describes type of operations performed by the web service and the messages involved in that operation.<protType> tag is used to define the port type.From the programming language point of view we can relate portType as Class or Function Library.

2 WSDL Messages: The message element defines the data elements of the operation.Each message can contain one or more parts.<part> tag is used to define part for the message. From the programming language point of view we can relate message parts as parameters in a function .

3 WSDL types: WSDL uses XML schema to define data types.All XSD data types can be used as WSDL types.

4 WSDL binding :Binding defines the message format and the protocal details for each port.SOAP is the basic protocol used for the bindings.