hypervisor（不管是什么类型）仅是一个从其来宾操作系统抽象机器硬件的分层应用程序。
So a hypervisor (regardless of the type) is just a layered application that abstracts the machine hardware from its guests.
在分层应用程序(J2EE应用程序通常属于此类)中，需要在所有层次执行授权——尤其是在最底层，这一点非常重要。
In layered applications, which J2EE applications frequently are, it is important to perform authorization at all layers — but particularly at the lowest layer.
在架构层，他们期望干净的应用程序分层，为了提高可修改性和可维护性。
At an architectural level, they desired clean application layering in order to improve modifiability and maintainability.
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