Applied XML Programming for Microsoft .NET.pdf - Csbdu.in

snapshot of the row as it was originally read, and the second node contains the currentvalues. The DiffGram represents a snapshot of the DataSet state and contents at agiven moment. To write DiffGrams, ADO.NET uses an XmlWriter object.The integration of and interaction between XML and ADO.NET classes is discussed inChapter 8.Application ConfigurationBefore Microsoft Windows 95, applications stored configuration settings to a text filewith a .ini extension. INI files store information using name/value pairs grouped undersections. Ultimately, an INI file is a collection of sections, with each section consisting ofany number of name/value pairs.Windows 95 revamped the role of the system registry—a centralized data repositoryoriginally introduced with Windows NT. The registry is a collection of binary files that theoperating system manages in exclusive mode. Client applications can read and writethe contents of the registry only by using a tailor-made API. The registry works as akind of hierarchical database consisting of root nodes (also known as hives), nodes,and entries. Each entry is a name/ value pair.All system, component, and application settings are supposed to be stored in theregistry. The registry continues to increase in size, contributing to the creation of aconfiguration subsystem with a single (and critical) point of failure. More recently,applications have been encouraged to store custom settings and preferences in a localfile stored in the application's root folder. For .NET Framework applications, thisconfiguration file is an XML file written according to a specific schema.In addition, the .NET Framework provides a specialized set of classes to read and writesettings. The key class is named AppSettingsReader and works as a kind of parser fora small fragment of XML code—mostly a node or two with a few attributes.ASP.NET applications store configuration settings in a file named web.config that islocated in the root of the application's virtual folder. Windows Forms applications, onthe other hand, store their preferences in a file with the same name as the executableplus a .config extension—for example, myprogram.exe.config. The CONFIG file mustbe available in the same folder as the main executable. The schema of the CONFIG fileis the same regardless of the application model.The contents of a CONFIG file is logically articulated into sections. The .NETFramework provides a number of predefined sections to accommodate Web andWindows Forms settings, remoting parameters, and ASP.NET run-time characteristicssuch as the authentication scheme and registered HTTP handlers and modules.User-defined applications can extend the XML schema of the CONFIG file by definingcustom sections with custom elements. By default, however, the AppSettingsReaderclass supports only settings expressed in a few formats, such as name/value pairs anda single tag with as many attributes as needed. This schema fits the bill in most cases,but when you have complex structured information, it soon becomes insufficient.Information is read from a section using special objects called section handlers. If nopredefined section structure fits your needs, you can provide a tailor-madeconfiguration section handler to read your own XML data, as shown here:10