WSDL Documents 

A WSDL document is a simple XML document which contains set of definitions to describe a web service. 

WSDL Document Structure 

A WSDL document consists below major elements:

The structure of a WSDL document as below:

<definitions>

<types>
   Definition of data type
</types>

<message>
   Definition of data 
</message>

<portType>
   Set of operations</portType>

<binding>
   Protocol and Data format specification
</binding>

</definitions>

A WSDL document also contain other elements, like extension elements, and a service element that makes it possible to group together definitions of several web services in one single WSDL document.

WSDL Ports

The <portType> element is most important WSDL element. It describes a web service operations that can be performed, and messages that are involved. 

WSDL Messages

The <message> element defines data elements of operation. Each message can consist of one or more parts. The parts can be compared to parameters of a function call in a traditional programming language.

WSDL Types

The <types> element defines data types that are used by web service.

For maximum platform neutrality, WSDL uses XML Schema syntax to define data types.

WSDL Bindings

The <binding> element defines data format and protocol for each port type.