说明：  ASP.NET2.0教程之三层开发.pdf，内容很清晰，对想初步了解ASP.NET三层结构的初学者绝对有参考价值，只有61页，可以很快看完。
(The three-tier development ASP.NET2.0 Tutorial. Pdf, content that is clear and would like a preliminary understanding of the three-tier structure of ASP.NET absolute beginners reference value, only 61 can be read quickly.)