Abstract: The progress of computer technology drives the progress of software systerm design. Practice proves layered design is the primary method to improve the usability and maintainability of software system. This paper introduces the concept of 3tier application and applies it to the development of .NET database operation system. Through the functional partitionings of presentation, business and data access, this paper realizes the best way of Microsoft .NET application to access data. At last the paper uses an example to describe the development course of .NET database operation system based on 3tier application in detail, and then probes how to realize an effective method to transmit data between tiers of distibuted application.

Key words: 3tier application, data access logic component, business entity component