This approach overcomes the security problems of deploying two-tier systems over the WAN by replicating a native client to a remote user.
通过将一个原生客户端复制给一个远程用户，这种途径克服了通过WAN部署两层系统的安全性问题。
And two-tier systems perform poorly when a fat client must connect to a database over the WAN.
当胖客户机必须通过WAN连接到数据库时，两层系统的性能较差。
Then there was another form of two-tier architecture in which not only the UI but even the business logic resided on the client tier.
此后又出现了另外一种2级结构，在这种结构中，不只是用户接口（UI），连业务逻辑也被放到了客户端一级。
Two-tier thick client applications are easy to develop, but any software upgrade because of changes in user interface or business logic has to be rolled out for all the clients.
尽管2级“胖客户端”应用的开发很简单，但是任何用户接口或者业务逻辑的改变所导致的软件升级都需要在所有客户端上进行。
Two-tier thick client applications are easy to develop, but any software upgrade because of changes in user interface or business logic has to be rolled out for all the clients.
尽管2级“胖客户端”应用的开发很简单，但是任何用户接口或者业务逻辑的改变所导致的软件升级都需要在所有客户端上进行。
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