英语论文网

三层体系架构的应用程序将业务逻辑、数据的处理、合法性验证等工作放到了中间层进行处理。一般来说，客户端是不会直接对数据库进行处理，而是通过数据访问层来建立连接，再经由业务逻辑层与数据库进行交互等工作。在三层结构的设计中，遵循了面向接口设计的思想，也就意味着三层结构之间的是向下依赖的，下一层对于上一层来说是“无知”的，当改变上一层的设计而不改变下一层的接口定义时对于其调用下一层来说是没有任何影响的。

Three-layer structure is simply between the client and the database adds a middle layer. The so-called three-tier system, was not referring to physical layer, not simply the three machines together is the three-tier architecture, three-tier architecture applications are not just in the C / S, B / S application procedure, where the three means is a logical layer. Three-tier architecture application business logic, data processing, etc. into the legality verification middle layer for processing. Typically, the client will not be processed directly to the database, but by the data access layer to establish a connection, and then interact with the database through the business logic work. The design of the three-tier structure, following the idea of oriented interface design, which means between the three-layer structure is dependent down, the next layer to the upper layer is "ignorant", and when changing the The design layer to the next level without changing the interface definition of the layer for which the call is no impact. So that developers can focus on one particular floor, and is easily replaced with a new layer of the original, so as to achieve good coordination division, the layers of code reuse and code updates. However, this layering system performance and reduces efficiency. Because if you do not use such a hierarchical structure, then many businesses will be able to directly access the database. Top-down hierarchical cascade may also lead to modifications.

Sql Server中的存储过程是一组被命名的存储在数据库中的为了完成特定功能的Transacation-Sql语句集。存储过程是可重复利用的一种方法,支持参数变量、条件执行以及其他的编程功能。应用程序能够通过存储过程的名字以及参数来调用执行存储过程。存储过程是数据库的一个重要的组成部分。

In Sql Server stored procedure is a set of named stored in the database in order to complete a specific function Transacation-Sql statement set. A stored procedure is a reusable method supports parameter variables, conditional execution, and other programming functions. Application can pass the stored procedure name and parameters to call the stored procedure. The database stored procedures is an important component.
A stored procedure is to use SQL Server provides a Transact-SQL language program statements. Transact-SQL language is mainly to provide variable declarations, ANSI-compliant SQL commands, the general flow control commands, internal functions and other functions to allow users to reference designed to meet the needs of the process. Stored by the application process by calling to execute, allow users to declare a variable, you can input and output parameters, execute the stored procedure returns the status value can also be nested calls. Stored procedures relative to other database access method has the following advantages:
(1) reusability. Call a stored procedure can be repeated, thus reducing the workload of database developers.
(2) efficiency. Stored procedure is created when it has been compiled, and general SQL statement executed once every need to compile once, so the stored procedure can be quickly implemented.
(3) cost-saving performance. After the stored procedure is compiled, stored in the database, when the network when the program calls the stored procedure simply pass the stored procedure name and parameters, thus reducing network