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CHAPTER 14 - Protection > 14.4 Access Matrix

14.4 Access Matrix

Our model of protection can be viewed abstractly as a matrix, called an access matrix. The rows of the access matrix represent domains, and the columns represent objects. Each entry in the matrix consists of a set of access rights. Because the column defines objects explicitly, we can omit the object name from the access right. The entry access(i,j) defines the set of operations that a process executing in domain Di can invoke on object Oj .
To illustrate these concepts, we consider the access matrix shown in Figure 14.3. There are four domains and four objects—three files (F1, F2, F3) and one laser printer. A process executing in domain D1 can read files F1 and F3. A process executing in domain D4 has the same privileges as one executing in domain D1; but in addition, it can also write onto files F1 and F3. Note that the laser printer can be accessed only by a process executing in domain D2.

  

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