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Data structure is the key to efficient storage of data in a computer system. Many types of database structures have been introduced to manage data in a suitable and investigatable manner. The most effective and efficient system is the one whose database structure is uncomplicated and flexible.
The Most popular form of database systems is relational database systems and these systems have become the dominant technology for database management. This model represents all data in the database in the form of simple two-dimensional tables called relations. Here, Information in more than one file can be easily extracted and combined. The strength of relational model is that it can relate data in any file or table to data in another file or table if they share a common data element and helps to produce reports. Three basic operations are used to develop useful sets of data: select, project and design. Relational database management systems depict many-to-many-relationship.
A relational database management system is just like a student-course relationship where each student can have multiple courses and each course has multiple students. University has many students and many courses. It uses implicit relationships-that can be implied from existing record data. Users and information specialists are freed from the need to identify all the information needs before creating the database. George W.Reynolds (1994) says that in case of relational database structure, table and table operations are well-defined because relational theory is based on set theory, relational algebra, and relational calculus.
While Hierarchal & network systems are older one. In theses systems one-to-many relationship is modeled which presents data in a tree-like structure. In network & hierarchal structure the link fields establish explicit relationship. Each record looks like an organizational chart. A hierarchal system is like a parent-child relationship. Parent can have multiple children but child has the same parent (Laudon & Laudon, 2007).
Relational database management systems are more flexible than hierarchal and network systems. These systems have become outdated because they do not support ad hoc, English language enquiries for information (O'Brien, 1999). In case of these outdated systems, all paths for accessing data must be specified in advance and changes can only be made by major programming effort (Laudon & Laudon, 2007). It confines the manager from making ad hoc requests-special requests for combinations of information not previously specified (MCleod R, 1997)
Relational database has much more flexibility in providing data for ad hoc queries, combining information from different sources, and providing capability to add new data and records without disturbing existing programs and applications. So, we can conclude that the success of relational database management systems lies on the flexible design and functioning of these systems.