Page 65 - 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%u062965dealing with The databases are very large, and it also has good retrieval and security measures. This model has disadvantages including: Lacks flexibility and good response to the user Complexity in application programming The data is stored in a hierarchical structure, and therefore it is difficult to change or modify this structure Network DBMS: The reticle data structure overcomes the obstacles of hierarchical formation, which does not allow a son to have more than one father. This type of database solves many problems of relationships, for example, we can assume that there is more than one supplier that supplies one spare part and also that each supplier is able to supply more than one type of spare parts, and these systems enable us to represent these relationships There is a variety of database management programs, there are database management packages that can handle the tree type, and there are packages that can handle the network type. Network database systems and hierarchical database systems are similar in that they require large memories. But they have many advantages, they are very efficient and handle very large amount of data but lack flexibility. Relational DBMS Relational databases appeared to solve the problems of hierarchical and network rules, and its idea is to look at the database as a set of tables or relationships called (relations), and the relationship represents a twodimensional table (rows and columns) the table symbolizes an entity and the rows represent a set of tables records. records or tuples), and columns represent the attributes of these tables or attributes; Each attribute must have a domain of values that this column can contain, and these tables are linked to each other by links, and each table must have a primary key; To distinguish rows from each other, the point where the row and column intersect (the adjective) is the value for that row. Table keys (relationships) are one of the most important characteristics of relational databases. As it is the characteristic of a particular table on the one hand, and the link that links the different tables with each other