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X ML has emerged as a de facto standard for data representation and transportation. No wonder that Microsoft has embraced it fully in their .NET Framework. This chapter provides an overview of what XML is and how it is related to the .NET Framework. Many of the topics discussed in this chapter might be already familiar to you. Nevertheless, I will cover them briefly here so as to form a common platform for further chapters. Specifically you will learn about the following: • Features and benefits of XML • Rules of XML grammar • Brief introduction to allied technologies such as DTD, XML schemas, parsers, XSLT, and XPath • Overview of the .NET Framework • Use of XML in the .NET Framework • Introduction to Visual Studio

C hapter 1 discussed two flavors of parsers—tree-based parsers and event-based parsers. You also learned that the Document Object Model (DOM) is a set of APIs for manipulating XML documents. This chapter covers the following topics: • System.Xml namespace classes related to DOM • Knowing when to use DOM • Reading an XML document by using DOM • Writing XML documents by using DOM • Creating a customized DOM-based parser by extending what is offered by .NET

C hapter 2 gave you a detailed understanding of the .NET Framework’s DOM parser, that is, the XmlDocument class. You also learned when to use DOM parsers. In this chapter, you are going to learn about XML reader and writer classes. The topics discussed include the following: • Using reader and writer classes • Knowing when to use these classes instead of DOM • Reading XML documents by using the XmlTextReader class • Writing XML documents by using the XmlTextWriter class • Working with a subset of XML documents and reader and writer classes

I n Chapters 2 and 3, you learned how to read and write XML documents by using the XmlDocument, XmlReader, and XmlWriter classes. These classes allow you to access the underlying documents, but by themselves they hardly provide a way to query and retrieve the data. That is why we need something that allows us to navigate, query, and retrieve data from XML documents easily and efficiently. The XPath standard is designed to do just that.

I n Chapters 2, 3, and 4, you learned how to read and write XML documents, though we always assumed that the XML structure (tag names, attribute names, nesting, and so on) contained in the source XML document was correct. However, in many real-world cases this assumption may not be true. For example, a purchase order application might be accepting orders from various customers in XML format. What is the guarantee that each submitted order adheres to the agreed-upon XML structure? What if somebody deviates from the agreed-upon structure? This is where XML schemas come into the picture.

I n the previous chapters, we dealt with XML documents and their manipulation. Our interaction with XML documents was limited to reading, writing, querying, and validating them with the help of .NET Framework classes. No doubt these operations are widely needed in real-world XML applications. However, often you also need to transform XML data from one representation to another. For example, you may need to convert XML data into HTML so that it can be displayed in the browser. So, how do we accomplish such a transformation? This is where Extensible Stylesheet Language Transformations (XSLT) comes into the picture.

A DO.NET is a technology for accessing and manipulating databases. Disconnected data access and XML integration are the key features of ADO.NET. In this chapter, you are going to see how ADO.NET has harnessed the power of XML in data representation. Specifically, this chapter covers the following: • An overview of XML integration in ADO.NET • Working with SqlDataReader and XML • DataSet architecture and disconnected data access • XML integration in DataSet • The XmlDataDocument class

Y our .NET applications consist of one or more classes. The objects of these classes are used to store state information. As long as your objects are available in the memory of your application, this state information is readily available. But what if you would like to persist object state across application shutdowns? At first you may think of saving object state in a database. However, databases generally store information in relational format, whereas objects often have a hierarchical structure. Moreover, you would need to create many tables in the database on your own. Storing object data in a database comes with its own overheads. Wouldn’t it be nice if the entire object state could be stored to a medium and retrieved later? That is what serialization offers.

T he idea of distributed application development is not new. Distributed technologies such as Distributed Component Object Model (DCOM), Remote Method Invocation (RMI), and Common Object Request Broker Architecture (CORBA) have existed for years. Applications based on Microsoft platforms commonly use DCOM, whereas Java-based applications use RMI and CORBA. However, none of these technologies is an unambiguous industry standard. That is where web services step in. Web services offer an industry standard for developing distributed and service-oriented applications, which are becoming more and more popular in modern computing.

M ost business applications store data in some kind of data store, which is usually a relational database. To that end, SQL Server is one of Microsoft’s flagship products. With the increasing use of XML in business applications, Microsoft found it necessary to incorporate strong support for XML in their database engine also, with SQL Server 2000 being possibly the first version where this XML integration was clearly visible.