WSDL stands for Web Services Description Language.
WSDL is a document written in XML. The document describes a Web service. It specifies the location of the service and the operations (or methods) the service exposes. WSDL is a suggestion by Ariba, IBM and Microsoft for describing services for the W3C XML Activity on XML Protocols.
W3C Publishes Working Drafts for Web Services Description Language (WSDL) 1.2. The World Wide Web Consortium (W3C) has announced the publication of initial working draft specifications for Web Services Description Language (WSDL) Version 1.2 and Web Services Description Language (WSDL) Version 1.2: Bindings. WSDL is "an XML format for describing network services as a set of endpoints operating on messages containing either document-oriented or procedure-oriented information. Work in progress at W3C indicates that WSDL might become a W3C Working Draft before the end of 2002, and an official Recommendation before the end of year 2003.
WSDL is accepted and supported by IBM, Microsoft, Macromedia and Ariba.
Let us discuss a bit on how web services are working. Web services can be created using any platforms for example, MS .NET or Sun ONE. Now it has to be registered in a UDDI service registry. While registering, the services should have the metadata about the service, that is, the necessary information about the service, explaining how to access and integrate the service. This metadata will be written in XML. This web service can be accessed by other web services who are also already registered in some UDDI registered,using SOAP,WSDL and XML. Here SOAP is used to access the components and WSDL to make the necessary bindings and to describe the service as a set of Ports. The ports help the service for input and output the messages that are for necessary interactions. Lets summarize the operations in a nutshell.
Accessing and using:
If you are a Microsoft developer already into web applications development you can learn .NET development tools. Java developers are in need to move into Sun ONE (Open Network Environment) / J2EE. But regardless of the tools and technology base you use to develop the web services, everyone should study and understand XML and XML based family of technologies.
Now you may ask " Where can we apply web services?" . A few examples now are like Stock price information gathering, whether reports, Flight reservations etc., As the technology explores many things are possible through web. Right now we have only tools and standards which are still not matured. Its yet to be simplified,and till then we have to work only with the technologies which are yet to improve a lot. But its needless to say that its time to learn and practice some web services development for any compant which is in web related development and its good if its now.