Introduction to Web Services Description Language (WSDL)

Web services description language - WSDL is a document that describes a Web service. Web services description language also specifies the location of the service and the operations (or methods) the service exposes. Web services description language is the description language for web services that describes a set of SOAP messages and how these messages are exchanged across network. Since Web services description language is in XML format it can be easily understood and edited by humans and machines.

While creating a complex web application with manifold web forms there is a need for the developers to make their task easier and execute the given project faster. They require services to avoid writing redundant code for their programs. Web services cater to the same need. A Web service is a broad term that represents the technology to transmit data over Internet or Intranet. This data can be accessed programmatically using open standards such as eXtensible Markup Language (XML), Simple Object Access Protocol (SOAP), Web services description language (WSDL), and Universal Discovery Description Integration (UDDI).

Another advantage of Web services description language being in XML format is that it is programming-language independent and also platform independent. In addition, Web services description language defines where the web service is available from and what communications protocol has been used to talk to the web service. As a result the Web services description language file describes everything that is required to write a program for an XML Web service.

There are tools available in Microsoft Visual Studio .NET to read a Web services description language file and generate the code required to communicate with an XML Web service. A Web services description language – WSDL document defines services as a collection of ports. A port can be said to be an association of a network address with a reusable binding. A web service can be described in web services description language using elements or tags such as <types>, <portType>, <message>, and <binding>.

The <types> element defines data types such as XML Schema that are supported by web service. They <portType> element is the primary element that defines a web service. In addition, it describes the operations that have to be performed and the messages concerned in a web service. The <message> element describes the data elements of the operation that has to be performed. There can be more than one part in a message. The <binding> element defines the format of the message and the protocol specification for each port.

Apart from all these major elements, a Web services description language - WSDL document can also contain elements such as extension elements and a service element. This makes all the definitions of multiple web services to group together in one single WSDL document.