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In the fields of physical security and information security, access control is the selective restriction of access to a place or other resource. The actof accessing may mean consuming, entering, or using. Permission to access a resource is called authorization (授权).
An access control mechanism (71) between a user (or a process executing on behalf of a user) and system resources, such as applications, operating systems, firewalls, routers, files, and databases. The system must first authenticate(验证)a user seeking access. Typically the authentication function determines whether the user is (72) to access the system at all. Then the access control function determines if the specific requested access by this user is permitted. A security administrator maintains an authorization database that specifies what type of access to which resources is allowed for this user. The access control function consults this database to determine whether to(73)access. An auditing function monitors and keeps a record of user accesses to system resources.
In practice, a number of(74)may cooperatively share the access control function. All operating systems have at least a rudimentary(基本的), and in many cases a quite robust, access control component. Add-on security packages can add to the(75)access control capabilities of the OS. Particular applications or utilities, such as a database management system, also
incorporate access control functions. External devices, such as firewalls, can also provide access control services.
A.components
B.users
C.mechanisms
D.algorithms
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考虑一个背包问题,共有n=5个物品,背包容量为W=10,物品的重量和价值分别为:w={2,2,6,5,4},v={6,3,5,4,6},求背包问题的最大装包价值。若此为0-1背包问题,分析该问题具有最优子结构,定义递归式为
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A.11
B.14
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