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.
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.
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
. White Pages
. Yellow Pages
. Green Pages
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.
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.