Английский язык: Аннотирование и реферирование текста

218 Table 2 A security matrix Users Data A Data B Data C User A Read Modify Execute Modify Read User A Read Modify Execute Execute User С Read Modify Read Execute Read Each row of the security matrix corresponds to a data item stored in the system. Each entry in the table lies at the intersection of a par- ticular row and a particular column. The entry tells what kind of access the person corresponding to the row in which the entry lies has to the data item corresponding to the column in which the entry lies. Usually, there are several kinds of access that can be specified. For instance, a person may be able to read a data item but not change it. Or he may be able to both read and modify it. If the data is a program, a person may be able to have the computer execute the program without being able either to read or modify it. Thus, people can be allowed to use programs without being able to change them or find out how they work. Needless to say, access to the security matrix itself must be re- stricted to one authorized person. Also, the software has to be reliable. Even the software issued by reputable vendors may be full of bugs. One or more bugs may make it possible for a person to circumvent the security system. The security provisions of more than one computer system have been evaded by high school and college students. Restricting the Console Operator . Most computer systems are extremely vulnerable to the console operator. That's because the opera- tor can use the switches on the computer's control panel to insert pro- grams of his own devising, to read in unauthorized programs, or to ex- amine and modify confidential information, including the security ma-