SOA, Web Service, SOAP and WSDL

“SOAP-oriented architecture”…!

Legacy Architecture

Service Oriented Architecture

Another example of SOA

Another Example for SOA

A service-oriented architecture (SOA) is a design model which relies on a collection of loosely coupled self-contained services that communicate with each other through the internet and can be called from multiple clients in a standard fashion. There are several commonly recognized benefits of SOA, including: scalability, security, simpler monitoring and auditing, standards reliance, interoperability across a range of resources, and plug-and-play interfaces (Maidment, 2008).

A common type of web service is the eXtensible Markup Language (XML) web service. There are two fundamental requirements for an XML web service: that it communicates via internet protocols and that it sends and receives XML formatted documents. XML is a markup language used to carry data and whose elements must be defined (thus making XML self-descriptive) (Erl, 2004).

Web services need to be defined in a consistent manner so that they can be discovered by and interfaced with other services and applications. The Web Services Description Language (WSDL) is a W3C specification which ensures that all web services are described in a consistent manner .
A WSDL service description describes the point of contact for a service, also known as the service endpoint or just endpoint. It establishes the physical location of the service and provides a formal definition of the endpoint interface so that programs wishing to communicate with the service know exactly how to structure the required request messages. Standardization is important so that all web services can be interfaced with other services and applications.
One implementation of an XML web service is a Simple Object Access Protocol (SOAP) service. A service is defined by four constructs: interface, message, service, and binding. The interface contains a series of constructs which contain operations. An operation represents single action or function which can be performed by the service. Messages represent input and output parameters for the operations.

WSDL binds SOAP and enables communication between different web services.

Skeleton SOAP Message

<?xml version="1.0"?>
<soap:Envelope
xmlns:soap="http://www.w3.org/2001/12/soap-envelope"
soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding">
<soap:Header>
...
</soap:Header>
<soap:Body>
...
  <soap:Fault>
  ...
  </soap:Fault>
</soap:Body>
</soap:Envelope>