Why Use XML Schemas?
To understand how schemas can help you, suppose that you write an application that accepts XML from another organization. To do this, you need to convey to the organization the required structure of the XML file so that they can provide you with XML data that can be parsed correctly. How would you do this? One method would be to e-mail the structure as: “The customer last name field should be a minimum of two characters and a maximum of 20 characters. The field is required.” Needless to say, this would be awkward and time consuming for any more than a moderate document. In addition, it would be inefficient if you need to update the XML format. Instead of risking breaking your application by malformed XML or having to rewrite the same implementation for another document, you can explicitly convey the structure in an XML schema. This also allows you to provide the structure to other departments and organizations so that they know how to format their XML document to effectively share data
