*What Is a Schema?

A schema is a "Structure", and the actual document or data that is represented through the schema is called "Document Instance". Those who are familiar with relational databases can map a schema to a Table Structure and a Document Instance to a record in a Table. And those who are familiar with object-oriented technology can map a schema to a Class Definition and map a Document Instance to an Object Instance.

A structure of an XML document can be defined as follows:

* Document Type Definition (DTDs)
* XML Schema Definition (XSD)
* XML Data Reduced (XDR) -proprietary to Microsoft Technology

We are specifically going to work with XML Schema Definitions (XSD).

*What Is XSD?

XSD provides the syntax and defines a way in which elements and attributes can be represented in a XML document. It also advocates that the given XML document should be of a specific format and specific data type.