The document discusses the Document Object Model (DOM) and XML classes for working with XML documents in .NET. It introduces LINQ to XML as an alternative to DOM that allows querying and modifying XML documents using LINQ. LINQ to XML enables functional construction of XML trees through querying and using results to construct XElement and XAttribute objects.

2.  Document Object Model (DOM) provide standards that
define the structure and a standard programming
interface that can be used in a wide variety of
environments and applications for XML documents.
 Classes that support the DOM are typically capable of
random access navigation and modification of the XML
document.
 The XML classes are accessible by setting a reference to
the System.Xml.dll file. The System.Data.dll file also
extends the System.Xml namespace.

3.  XmlDocument
 XmlDataDocument
 XPathDocument
 XmlConvert
 XPathNavigator
 XmlNodeReader
 XmlTextReader
 XmlTextWriter
 XmlReader
 XslTransform

4.  The XML Classes
 Creating a New XmlDocument from Scratch
 Parsing XmlDocuments (using DOM and
XPathNavigator)
 Searching the XmlDocument (using DOM and
XPathNavigator)
 Writing an XML File Using the XmlTextWriter
 Reading an XML File Using the XmlTextReader
 Modifying an XML Document
 Validating XML Documents
 Using LINQ to XML

5.  LINQ to XML is a LINQ-enabled, in-memory XML
programming interface that enables you to work with XML
from within the .NET Framework programming languages.
 LINQ to XML is like the Document Object Model (DOM) in
that it brings the XML document into memory. You can
query and modify the document, and after you modify it
you can save it to a file or serialize it and send it over the
Internet. However, LINQ to XML differs from DOM: It
provides a new object model that is lighter weight
and easier to work with, and that takes advantage of
language improvements in Visual C# 2008.

6.  The most important advantage of LINQ to XML is its
integration with Language-Integrated Query (LINQ). This
integration enables you to write queries on the in-memory
XML document to retrieve collections of elements and
attributes. The query capability of LINQ to XML is
comparable in functionality (although not in syntax) to
XPath and XQuery. The integration of LINQ in Visual C#
2008 provides stronger typing, compile-time checking, and
improved debugger support.
 Another advantage of LINQ to XML is the ability to use
query results as parameters to XElement and XAttribute
object constructors enables a powerful approach to creating
XML trees. This approach, called functional construction,
enables developers to easily transform XML trees from one
shape to another.

7. IEnumerable<XElement> partNos = from item in
purchaseOrder.Descendants("Item") where (int)
item.Element("Quantity") * (decimal)
item.Element("USPrice") > 100 orderby
(string)item.Element("PartNumber") select item;