【正文】 almost all existing ASP pages will have to be modified to some extent in order to run under . In addition, major changes to Visual Basic .NET mean that existing ASP pages written with Visual Basic Scripting Edition typically will not port directly to . In most cases, though, the necessary changes will involve only a few lines of code. ? Accessing databases from applications is an oftenused technique for displaying data to Web site visitors. makes it easier than ever to access databases for this purpose. It also allows you to manage the database from your code. ? provides a simple model that enables Web developers to write logic that runs at the application level. Developers can write this code in the text file or in a piled class deployed as an assembly. This logic can include applicationlevel events, but developers can easily extend this model to suit the needs of their Web application. ? provides easytouse application and sessionstate facilities that are familiar to ASP developers and are readily patible with all other .NET Framework APIs. ? For advanced developers who want to use APIs as powerful as the ISAPI programming interfaces that were included with previous versions of ASP, offers the IHttpHandler and IHttpModule interfaces. Implementing the IHttpHandler interface gives you a means of interacting with the lowlevel request and response services of the IIS Web server and provides functionality much like ISAPI extensions, but with a simpler programming model. Implementing the IHttpModule interface allows you to include custom events that participate in every request made to your application. ? takes advantage of performance enhancements found in the .NET Framework and mon language runtime. Additionally, it has been designed to offer significant performance improvements over ASP and other Web development platforms. All code is piled, rather than interpreted, which allows early binding, strong typing, and justintime (JIT) pilation to native code, to name only a few of its benefits. is also easily factorable,。 you can author applications in any .NET patible language, including Visual Basic .NET, C, and JScript .NET. Additionally, the entire .NET Framework is available to any application. Developers can easily access the benefits of these technologies, which include the managed mon language runtime environment, type safety, inheritance, and so on. has been designed to work seamlessly with WYSIWYG HTML editors and other programming tools, including Microsoft Visual Studio .NET. Not only does this make Web development easier, but it also provides all the benefits that these tools have to offer, including a GUI that developers can use to drop server controls onto a Web page and fully integrated debugging support. Developers can use Web Forms or XML Web services when creating an application, or bine these in any way they see fit. Each is supported by the same infrastructure that allows you to use authentication schemes, cache frequently used data, or customize your application39。s best enterprise servers that support runtime hosting. Overview of provides consistent access to data sources such as Microsoft SQL Server, as well as data sources exposed through OLE DB and XML. Datasharing consumer applications can use to connect to these data sources and retrieve, manipulate, and update data. cleanly factors data access from data manipulation into discrete ponents that can be used separately or in tandem. includes .NET Framework data providers for connecting to a database, executing mands, and retrieving results. Those results are either processed directly, or placed in an DataSet object in order to be exposed to the user in an adhoc manner, bined with data from multiple sources, or remoted between tiers. The DataSet object can also be used independently of a .NET Framework data provider to manage data local to the application or sourced from XML. The classes are found in , and are integrated with the XML classes found in . When piling code that uses the namespace, reference both and . XML and leverages the power of XML to provide disconnected access to data. was designed handinhand with the XML classes in the .NET Framework — both are ponents of a single architecture. and the XML classes in the .NET Framework converge in the DataSet object. The DataSet can be populated with data from an XML source, whether it is a file or an XML stream. The DataSet can be written as World Wide Web Consortium (W3C) pliant XML, including its schema as XML Schema definition language (XSD) schema, regardless of the source of the data in the DataSet. Because the native serialization format of the DataSet is XML, it is an excellent medium for moving data between tiers making the DataSet an optimal choice for remoting data and schema context to and from an XML Web service. Components The ponents have been designed to factor data access from data manipulation. There are two central ponents of that acplish this: the DataSet, and the .NET Framework data provider, which is a set of ponents including the Connection, Command, DataReader, and DataAdapter objects. The DataSet is the core ponent of the disconnected architecture of . The DataSet is explicitly designed for data access independent of any data source. As a result it can be used with multiple and differing data sources, used with XML data, or used to manage data local to the application. The DataSet contains a collection of one or more DataTable objects made up of rows and columns of data, as well as primary key, foreign key, constraint, and relation information about the data in the DataTable objects. The other core element of the architecture is the .NET Framework data provider, whose ponents are explicitly designed for data manipulati