Instead the support staff assigned to each department

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Unformatted text preview: organizing data, a set of programs is provided to facilitate the users in organizing, creating, deleting, updating, and manipulating their data in a database. All these programs together form a Database Management System (DBMS). The commonly supported features in a typical database management system are described below. Database Models We saw that multiple related files are integrated together to form a database. A database model defines the manner in which the various files of a database are linked together. The four commonly used database models are (they are also known as database structures or database structuring techniques): 1. Hierarchical, 2. Network, 3. Relational, and 4. Object-oriented They are briefly described below. Hierarchical Databases In a hierarchical database, the data elements are linked in the form of an inverted tree structure with the root at the top and the branches formed below. Below the single-root data element are subordinate elements, each of which, in turn, has one or more other elements. There is a parent-child relationship among the data elements of a hierarchical database. A parent data element is one that has one or more subordinate data elements. The data elements that are below a parent data element are its children data elements. There may be many children elements under each parent element, but there can be only one parent element for any child element. Note that the branches in a tree structure are not connected. An example of a hierarchical database structure is shown in Figure 16.7. The hierarchical database structure has been used in a large number of database applications because the data elements of many applications can be neatly organized in the form of a hierarchical tree structure. However, the main limitation of a hierarchical database structure is that it does not support flexible data access because the data elements can be accessed only by following the path down the tree structure. Hence it is important to determine all ty...
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This document was uploaded on 04/07/2014.

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