Data Models in the Database Management System (DBMS)are divided into three categories. These are as follows −
Object Model − It uses concepts like entities, attributes, and their relationship. This model can be used to describe the data at the conceptual and external level. For Example: E-R model.
Physical Model − These models describe how the data is stored in the computer. This model is used to describe the data at the internal level.
Record based logical models − These models are used in describing the data at the logical and view level. It is used to specify the overall logical structure of the database.
The features of hierarchical model are as follows −
It is based on tree structure.
It consists of a collection of records that are connected to each other by links.
The tree structure used in hierarchical models is called as routed true.
The root node of that tree is an empty node.
So, Hierarchical model is a collection of routed trees and the relationship that exists in the hierarchical model is one to many and one to one.
The advantages of hierarchical model are as follows −
It is easy to understand.
More efficient than the ER model.
The disadvantages of hierarchical model are as follows −
Data inconsistency occurs when the parent node is deleting that result in the deletion of the child node.
Wastage of storage space.
Complex to design.
Absence of structural independence.
Given below is an example of the hierarchical model in pictorial format −