Hierarchical Model in DBMS – Dr. Balvinder Taneja

1. Introduction to the Hierarchical Model

The Hierarchical Model is a database model that organizes data in a tree-like structure, where each record has a single parent but can have multiple children. It was one of the earliest models used in database management systems (DBMS) and was widely implemented in IBM’s Information Management System (IMS).

Key Features of the Hierarchical Model

✅ Tree Structure → Data is organized in a hierarchy (parent-child relationship).
✅ One-to-Many Relationship → Each parent can have multiple children, but each child has only one parent.
✅ Fast Access → Efficient for retrieving structured data with predefined relationships.
✅ Navigational Model → Data is accessed using pointers, requiring step-by-step traversal from the root.

2. Structure of the Hierarchical Model

The Hierarchical Model follows a tree structure, with:

Root Node → The top-most record (e.g., “Company” in an Employee Database).
Parent Nodes → Nodes that have one or more child nodes (e.g., “Departments” under “Company”).
Child Nodes → Nodes that belong to a specific parent (e.g., “Employees” under “Departments”).

Example: Employee Database in Hierarchical Model

Company  
├── HR Department  
│   ├── Employee 1  
│   ├── Employee 2  
├── IT Department  
│   ├── Employee 3  
│   ├── Employee 4

Table Representation of the Hierarchical Model

Parent (Department_ID)	Child (Employee_ID)
HR	E1
HR	E2
IT	E3
IT	E4

In this example:

HR and IT are parent nodes.
Each Employee (E1, E2, E3, E4) is a child node.
Each Employee belongs to only one department.

3. Working of the Hierarchical Model

How Data is Accessed?

Data retrieval follows a top-to-bottom approach.
To access a child node, the system traverses from the root node using pointers.
Queries require navigational access, meaning they must follow the hierarchy.

How Data is Stored?

Data is stored using records and links (pointers).
Each record (node) has one parent link and multiple child links.

4. Advantages of the Hierarchical Model

✅ 1. Fast and Efficient Data Retrieval

Since data is predefined in a tree structure, searches are quick and efficient.
Used in real-time applications like airline reservations and banking systems.

✅ 2. Data Integrity & Security

Enforces strict parent-child relationships, ensuring data consistency.
Only authorized paths allow access to data.

✅ 3. Easy to Maintain Relationships

Natural Hierarchy fits well with real-world applications, such as organization charts or file systems.

✅ 4. Reduces Redundancy

Data does not get duplicated since child records belong to a single parent.

5. Disadvantages of the Hierarchical Model

❌ 1. Complex to Modify

Adding, deleting, or modifying a record requires restructuring the entire hierarchy.
Example: If we want to move “Employee 3” to the “HR Department”, it requires restructuring the hierarchy.

❌ 2. One-to-Many Limitation

A child cannot have multiple parents.
Example: If “Employee 1” belongs to both “HR” and “IT”, this structure cannot represent the relationship.

❌ 3. Difficult Query Processing

Queries must follow a predefined path, making complex queries difficult.
Unlike relational databases, we cannot use SQL-style flexible queries.

❌ 4. Poor Flexibility

Many-to-Many relationships are not possible without duplicating data.
Example: If an “Employee” works in multiple projects under different departments, the structure fails.

6. Applications of the Hierarchical Model

Despite its limitations, the Hierarchical Model is still used in specific applications where a strict one-to-many relationship is necessary.

1. Banking Systems

Customer Accounts Hierarchy → A bank maintains customer records under different account types.

2. File Systems (Windows, Linux, macOS)

Folder Structure follows a hierarchical tree model.mathematicaCopyEditRoot Directory ├── Program Files │ ├── Microsoft Office │ ├── Adobe Photoshop ├── Users │ ├── User1 │ ├── User2

3. Airline Reservation Systems

Flights, Tickets, and Passengers are organized in a hierarchical structure.

4. Organizational Charts

Used to manage employee hierarchy in companies.

7. Comparison: Hierarchical vs. Other Models

Feature	Hierarchical Model	Relational Model	Network Model
Structure	Tree-like	Tables	Graph-like
Relationships	One-to-Many	Many-to-Many	Many-to-Many
Data Access	Navigational	SQL Queries	Navigational
Flexibility	Low	High	Medium
Query Processing	Complex	Simple (SQL)	Moderate

8. Conclusion

The Hierarchical Model is a structured and efficient way of organizing one-to-many relationships in databases. However, due to rigid structure and difficult modifications, it has been mostly replaced by the Relational Model (RDBMS) in modern applications.

However, it is still used in legacy systems, file systems, and banking applications where strict hierarchical relationships are needed.

Summary of the Hierarchical Model

✅ Best for structured, well-defined data
✅ Fast and secure for specific applications
❌ Hard to modify and lacks flexibility
❌ Not suitable for many-to-many relationships