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

applications, XML.serialization is key technology that you must absolutely be familiarwith. We'll examine XML serialization in Chapter 11.Let's look now at how ADO.NET and XML classes can be used to read and processrelational data expressed in a hierarchical shape.XML Data Readers.NET Framework applications delegate all their low-level data access tasks to a specialbreed of connector objects called managed data providers. The object model aroundthese connector components is known as ADO.NET. Basically, a data provider is thesoftware component that enables any .NET Framework application to connect to a datasource and execute commands to retrieve and modify data.A .NET Framework data provider component interfaces client applications through theobjects in the ADO.NET namespace and exposes any provider-specific behaviordirectly to consumers. A .NET Framework data provider component creates a minimallayer between the physical data source and the client code, thereby increasingperformance without sacrificing functionality.A .NET Framework data provider is fully integrated with the surrounding environment—the .NET Framework—so any results that a command generates are promptly andautomatically packed into a familiar data structure—the ADO.NET and XML classes—for further use.A key architectural goal for .NET Framework data providers is that they must bedesigned to work on a rigorous per-data source basis. They expose connection,transaction, command, and reader objects, all working according to the internalcapabilities and structure of the DBMS. As a result, the programming interface of, say,the Microsoft Access data provider will not be completely identical to that of the SQLServer provider. An area in which this difference is palpable is in XML data queries.OLE DB and .NET Framework Managed Data ProvidersPrior to the advent of the .NET Framework, OLE DB was considered the emergingdata access technology. It was well positioned to definitively replace in the heart, andthe code, of developers another well-known standard for universal data access—opendatabase connectivity (ODBC).OLE DB is the data access technology that translates the Universal Data Access(UDA) vision into concrete programming calls. Introduced about five years ago, UDAdescribes a scenario in which all the data that can be expressed in a tabular formatcan be accessed and manipulated through a common API, no matter the actual binaryformat and the storage medium. According to the UDA vision, special modules—theOLE DB providers—would be called to expose the contents of a data source to theworld. Another family of components—the OLE DB consumers—would consume suchcontents by interacting with the providers through a common API.In designing the intermediate API for OLE DB providers and consumers tocommunicate through, Microsoft decided to use the key software technology of thetime: the Component Object Model (COM). In this design approach, the consumer had293