XML is central to data exchange between applications in the .NET Framework.
To enable disparate systems to communicate with each other, we require a standard that is understandable by all systems. Therefore, the obvious choice is a standard that is text-based. Because most systems understand text-based data, XML is the preferred standard of communication.

A well-formed XML document can have an associated document type definition (DTD) or an XML Schema that describes the data and the relationship between the data within an XML document. DTDs define the grammar for a class of XML documents. DTDs have a syntax that is different from the syntax of XML. XML Schema, on the other hand, is an XML document that describes the elements and attributes of an XML document and can include type information.

The XML Document Object Model

The XML Document Object Model (XML DOM) class is a representation of the XML document in memory. The DOM class lets you read, write, and manipulate an XML document. The .NET Framework provides classes, which enable you to navigate through an XML document and obtain relevant information. Every XML document consists of parent and child nodes.