Web Services, XML, WSDL & SOAP

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A simple web application providing HTTP (GET/POST) request-response routines can also be called a service. But definition for this request-response routine could be confusing to the consumers of the service. SOA clearly outlines that definition or meta data of a service should be clearly defined and implemented so that the consumer writers do not have problem in understanding and using the service. This is called discoverability in SOA jargon.

This is the reason XML became popular de facto standard for publishing the services. There are two XML components that form a service

• SOAP: used for request – response data packaging.
• WSDL: used for Service definition

The combination of SOAP and WSDL has become analogous for web services. And services in SOA are usually web services.

However it should be understood that web service is not the only form of SOA and other services can also be part of an SOA like

• Common Object Request Broker Architecture (CORBA) or
• Component Object Model (COM)

A service need not be middle tier only. It can be any tier including data access layer and UI layer.

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