WSDL

WSDL (often pronounced whiz-dull) stands for Web Services Description Language.
For our purposes, we can say that a WSDL file is an XML document that describes a set of SOAP messages and how the messages are exchanged. In other words, WSDL is to SOAP what IDL is to CORBA or COM. Since WSDL is XML, it is readable and editable but in most cases, it is generated and consumed by software.

Read About ☛ UDDI: (Universal Discovery Description and Integration)

Value Of WSDL:

To see the value of WSDL, imagine you want to start calling a SOAP method provided by one of your business partners. You could ask him for some sample SOAP messages and write your application to produce and consume messages that look like the samples, but this can be error-prone. For example, you might see a customer ID of 2837 and assume it's an integer when in fact it's a string. WSDL specifies what a request message must contain and what the response message will look like in unambiguous notation.
The notation that a WSDL file uses to describe message formats is based on the XML Schema standard which means it is both programming-language neutral and standards-based which makes it suitable for describing XML Web services interfaces that are accessible from a wide variety of platforms and programming languages. In addition to describing message contents, WSDL defines where the service is available and what communications protocol is used to talk to the service. This means that the WSDL file defines everything required to write a program to work with an XML Web service. There are several tools available to read a WSDL file and generate the code required to communicate with an XML Web service. Some of the most capable of these tools are in Microsoft Visual Studio® .NET.

Read About ☛ SOAP (Simple Object Access Protocol)

Many current SOAP toolkits include tools to generate WSDL files from existing program interfaces, but there are few tools for writing WSDL directly, and tool support for WSDL isn't as complete as it should be. It shouldn't be long before tools to author WSDL files, and then generate proxies and stubs much like COM IDL tools, will be part of most SOAP implementations. At that point, WSDL will become the preferred way to author SOAP interfaces for XML Web services.

Read About ☛ XML Web Service: