Hence many users find the relational database model

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Unformatted text preview: s structure that in this semester, Maths course has been taken by Seeta, Geeta, Ram and Sohan, and it is also easy t tell that in this semester, Geeta has taken the courses Hindi, Maths and Computer Science. The example also shows a child element that has no parent element (the student named Raju he might be a research student who has not taken any course in this semester). Relational Databases In a relational database, the data elements are organized in the form of multiple tables with rows and columns. Each table of the database is stored as a separate file. Each table column represents a data field, and each row a data record (also knows as a tuple). The data in one table (or file) is related to data in another table through the use of a common field. An example of a relational database structure is shown in Figure 16.9. The example shows a sample library database comprised of three tables. The first table contains the data of library members, the second table contains the data of borrowed books, and the third table contains the data of books in the library. Each new member assigned a membership number and issued a library card with this number on it. The member's name, address, and membership number are added to the first table. When a member borrows a book, the membership number of the borrower, the book's ISBN number (which serves as the unique identification number for a book), and the due date for returning the book are added to the second table. The first and second tables are related through the 'Membership No.' common field, and the second and third tables are related through the "Book No.' common field. Now suppose the librarian wants a report of overdue books as of 10-11-2001, and wants the list to contain the borrower's details and the book's details for each overdue book. To produce such a report, the database search routine will first search for the due date field in the borrowed books data table to surface the three overdue books. The database management system will then use the 'Membership No.' field to cross-reference the borrower's details for each overdue b...
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This document was uploaded on 04/07/2014.

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