The DOM stands for Document Object Model, which describes the logical formation of documents and provides the way to access and manipulate a document. It supplies an Application Programming Interface (API) to XML documents. It is built around the object-oriented design; therefore, it is known as DOM. The DOM model considers an XML document as a composition of objects and every object consists of properties and behaviors that can be manipulated by the DOM methods. The DOM allows creating and building XML documents, navigating the structure of documents, and managing the elements and their data. You can use the DOM methods and objects with any language, such as C#, VB, JavaScript, and VBScript

The System.xml.dll is the real physical file, which contains the XML implementation. Some of the other namespaces that allow .NET to use XML are as follows:
• System.Xml
• System.Xml.Schema
• System.Xml.XPath
• System.Xml.Xsl

The following are two main types of XML parsers:
• Tree-based API - Compiles an XML document into a tree structure and loads it into memory. You can traverse and change the tree structure. The DOM is an example of a tree-based API.
• Event-based API - Provides the report to an application about the parsing events by a set of built-in callback functions. An example of the event-based API is SAX.

The XmlReader class is used to read XML data in a fast, forward-only, and non-cached manner.
To work with XmlReader class in .NET, you need to import the following namespace:

In C#:
using System.Xml;

In VB:
Imports System.Xml

The XmlWriter class is used to write XML to a stream, a file, or a Textwriter object. This class works in a forward-only, non-cached manner. You can configure the XmlWriter object up to a large extent. With this object, you can specify a few things, such as whether to indent content or not, the amount to indent, what quote character to use in attribute values, and whether or not namespaces are supported.