Page 62 - Demo

%u062c%u0645%u064a%u0639 %u0627%u0644%u062d%u0642%u0648%u0642 %u0645%u062d%u0641%u0648%u0638%u0629 %u0640 %u0627%u0625%u0644%u0639%u062a%u062f%u0627%u0621 %u0639%u0649%u0644 %u062d%u0642 %u0627%u0645%u0644%u0624%u0644%u0641 %u0628%u0627%u0644%u0646%u0633%u062e %u0623%u0648 %u0627%u0644%u0637%u0628%u0627%u0639%u0629 %u064a%u0639%u0631%u0636 %u0641%u0627%u0639%u0644%u0647 %u0644%u0644%u0645%u0633%u0627%u0626%u0644%u0629 %u0627%u0644%u0642%u0627%u0646%u0648%u0646%u064a%u062962information from the risks of interference, breach or theft. In light of this, the database system can be defined as %u201can orderly collection of data and program records with the least possible amount of repetition and the greatest available data integrity while allowing sharing of data for different users without the slightest link between data and application programs. The difference between database systems and traditional file systems There are many characteristics that differentiate between databases and traditional file systems, which are: Self-Description Nature: Databases contain data and describe data by creating a data index that contains what is called (Meta-data). - Separation between programs and data (Program/Data Insulation): The programs do not contain a description of the data, but rather there is a separation between them, which allows the possibility of modifying the form of the data without the need to modify the programs. Sharing data and dealing with many users (Data Sharing and Multi-user system): Databases allow sharing in the use of data, as well as giving the ability for many users to interact with the same databases at the same time without problems. Database levels: Databases can be visualized on three levels, the level closest to the user is the external level where the user deals with the stored data, so this level focuses on how the data is presented to the user, and the second level is the internal level and focuses on how the data is stored. Between the user level and the storage level, there is a third level, which is the logical level, as shown in the following figure. It is clear from the figure that there is no direct link between the three levels, which made the separation between these levels possible. The user can change his programs without changing the database. And between each level and the next, there is a kind of mapping to describe the data between the two levels to ensure the presence of data and the possibility of isolation between the stored data and the user level and to break any link between them.