Web Services Description Language (WSDL) is one of the prime specifications in web services, the other two being SOAP and UDDI. WSDL is the description language for web services that describes a set of SOAP messages and how these messages are exchanged across network. WSDL will be in XML format; therefore it can be easily understood and edited by humans and machines.
Another advantage of WSDL being in XML format is that it is programming-language independent and also platform independent. In addition, WSDL 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 WSDL 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 WSDL file and generate the code required to communicate with an XML Web service.
Universal Discovery Description Language (UDDI) is a directory where you can expose your web services for other users to easily access it. You can also consume the web service that is already posted in UDDI. However, you can also post a web service without registering it in UDDI. DISCO is another directory where you can post your web service. But if you want to reach to maximum of customers, you can place it in UDDI. The UDDI directory offers three parts for you to register:
• White Pages
• Yellow Pages
• Green Pages
The white pages consist of the description such as name and address of the company offering the service. The yellow pages consist of industrial categories based on standard taxonomies such as North American Industry Classification System and Standard Industrial Classification. The green pages describe the interface to the web service in detail so that anyone can write an application after using the web service. Web services are described in UDDI directory through a document called Type Model or tmodel. Normally, this tModel contains a WSDL file that describes a SOAP interface to an XML Web service, but the tModel is flexible enough to describe almost any kind of web service.
Apart from using the web services from UDDI, you can also search a particular web service in UDDI. In addition, you can search for companies’ information that posted web services. In certain times, you might know the names of the companies that offer web services but you may not be aware of the web services that they offer. The WS-Inspection is a specification in UDDI that allows you to search for a collection of web services that are located in a particular company name. You can evaluate these web services according to your requirements.