Wrap-Up

In this chapter, we studied Extensible Markup Language and several of its related technologies. We began by discussing some basic XML terminology, introducing the concepts of markup, XML vocabularies and XML parsers (validating and nonvalidating). We then demonstrated how to describe and structure data in XML, illustrating these points with examples marking up an article and a business letter.

The chapter discussed the concept of an XML namespace. You learned that each namespace has a unique name that provides a means for document authors to unambiguously refer to elements with the same name (i.e., prevent naming collisions). We presented examples of defining two namespaces in the same document, as well as setting the default namespace for a document.

We also discussed how to create DTDs and schemas for specifying and validating the structure of an XML document. We showed how to use various tools to confirm whether XML documents are valid (i.e., conform to a DTD or schema).

The chapter also demonstrated how to create and use XSL documents to specify rules for converting XML documents between formats. Specifically, you learned how to format and sort XML data as XHTML for display in a Web browser.

The final sections of the chapter presented more advanced uses of XML in C# applications. We demonstrated how to retrieve and display data from an XML document using various classes of the .NET Framework. We illustrated how a Document Object Model (DOM) tree represents each element of an XML document as a node in the tree. The chapter also demonstrated reading data from an XML document using the XmlReader class, displaying DOM trees graphically and locating data in XML documents with XPath. Finally, we showed how to use .NET Framework classes XmlReader and XslCompiledTransform to perform schema validation and XSL transformations, respectively.

In Chapter 20, we begin our discussion of databases, which organize data in such a way that the data can be selected and updated quickly. We introduce Structured Query Language (SQL) for writing simple database queries (i.e., searches) and ADO.NET for manipulating information in a database through C#. You will learn how to create XML documents based on data in a database.