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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.
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):
3. Relational, and
They are briefly described below.
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.
- Spring '14