An application server provides access to the data for the client. It serves as an
interface between the client and one or more database servers, which provides an
additional level of security. It can also perform some of the query processing for the
client, thus removing some of the load from the database server.

The application server assumes the identity of the client when it is performing
operations on the database server for that client. The application server’s privileges
are restricted to prevent it from performing unneeded and unwanted operations during a
client operation.

应用服务器
应用服务器负责为客户端访问数据。应用服务器作为客户端与数据库服务器间的接口，能够提供额外的
安全性控制。应用服务器还能为客户端进行一定的数据处理工作，这减轻了数据库服务器的工作负载。