From http://www.w3schools.com (Copyright Refsnes Data)
This tutorial has taught you how to describe the structure of an XML document.
You have learned how to use an XML Schema is to define the legal elements of an XML document, just like a DTD. We think that very soon XML Schemas will be used in most Web applications as a replacement for DTDs.
You have also learned that the XML Schema language is very rich. Unlike DTDs, it supports data types and namespaces.
For more information on XML Schema, please look at our XML Schema reference.
The next step is to learn about WSDL.
WSDL is a schema-based language for describing Web services and how to access them.
WSDL describes a web service, along with the message format and protocol details for the web service.
If you want to learn more about WSDL, please visit our WSDL tutorial.
From http://www.w3schools.com (Copyright Refsnes Data)