Since security is one of the central problems in computer science,the restudy of these typical models are very important for us to seize the essentials of computer security.

• 目前,共享计算机系统的安全问题仍然是计算机科学的中心问题之一,研究这些经典模型,对于我们全面理解计算机系统的安全问题,展望未来发展方向,具有重要意义。