4 the system administration and maintenance cost is

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Unformatted text preview: themselves to the database system in order to obtain access to all or part of the data in the database. 3. Many database management systems support a program-level of security that precludes unauthorized users from using particular programs that access the database. 4. Many database management systems support record-level security that prevents unauthorized users from accessing or updating certain records, such as employee records of top-level managers in an employee database. 5. Many database management systems even support field-level security that prevents unauthorized users from accessing or updating sensitive information in certain fields, such as salary. 6. Many database management systems support read-only access that prevents unauthorized users from modifying certain information (they can only view the information). 7. All database management systems maintain a log of database accesses so that in case of any security breach, the log records can be analyzed to detect the possible cause of the problem. Client-Server Database Systems With the proliferation of computer networks, it became possible to access the data stored in a database from any system connected to the same network on which the system having the database was located. This gave birth to the client-server model of database systems. As shown in Figure 16.20, in this model the database is stored at and managed by a computer system called the database server. It runs all important modules of the database management system that deal with the maintenance and processing of data (called server programs). On the other hand, systems on the same network that are primarily meant for accessing data from the database are called database clients. They serve as front-end systems to the database and run those modules (called client programs) of the database management system that facilitate specification of access requests. When a database client needs some information from the database, it makes a request to the database server. The request trav...
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