DBMS Data Models – Hierarchical, Network, Relational & Object-Oriented

Data models define how data is stored, organized, and manipulated in a database. They provide a conceptual framework to represent real-world entities and relationships.

1. Hierarchical Data Model

Data is organized in a tree structure with parent-child relationships. Each child has only one parent.

-- Oracle Example: Department → Employee
CREATE TABLE department (
  dept_id NUMBER PRIMARY KEY,
  dept_name VARCHAR2(50)
);

CREATE TABLE employee (
  emp_id NUMBER PRIMARY KEY,
  emp_name VARCHAR2(50),
  dept_id NUMBER REFERENCES department(dept_id)
);

SELECT d.dept_name, e.emp_name
FROM department d
JOIN employee e ON d.dept_id = e.dept_id
ORDER BY d.dept_id;

2. Network Data Model

Data is represented as records (nodes) and links (edges), supporting many-to-many relationships.

-- Oracle Example: Employee ↔ Project
CREATE TABLE project (
  project_id NUMBER PRIMARY KEY,
  project_name VARCHAR2(50)
);

CREATE TABLE employee (
  emp_id NUMBER PRIMARY KEY,
  emp_name VARCHAR2(50)
);

CREATE TABLE project_assignment (
  project_id NUMBER REFERENCES project(project_id),
  emp_id NUMBER REFERENCES employee(emp_id),
  PRIMARY KEY(project_id, emp_id)
);

3. Relational Data Model

Data is stored in tables (relations) with rows (tuples) and columns (attributes). Relationships are defined with primary and foreign keys.

-- Oracle Example: Student / Course / Enrollment
CREATE TABLE student (
  student_id NUMBER PRIMARY KEY,
  name VARCHAR2(50),
  course VARCHAR2(50)
);

CREATE TABLE course (
  course_id NUMBER PRIMARY KEY,
  title VARCHAR2(50)
);

CREATE TABLE enrollment (
  student_id NUMBER REFERENCES student(student_id),
  course_id NUMBER REFERENCES course(course_id),
  PRIMARY KEY(student_id, course_id)
);

4. Object-Oriented Data Model

Integrates object-oriented programming concepts into database storage. Stores objects, attributes, and methods.

-- Oracle Object Type Example
CREATE TYPE Student_Type AS OBJECT (
  student_id NUMBER,
  name VARCHAR2(50),
  course VARCHAR2(50),
  MEMBER FUNCTION getDetails RETURN VARCHAR2
);
/

CREATE TABLE Student_Obj OF Student_Type;

INSERT INTO Student_Obj VALUES (Student_Type(101, 'Ahsan', 'DBMS'));

Comparison Table

Feature	Hierarchical	Network	Relational	Object-Oriented
Structure	Tree	Graph	Table	Objects / Classes
Relationships	1-to-many	Many-to-many	Any via keys	Any via objects
Flexibility	Low	Medium	High	High
Oracle Example	Dept → Employee	Employee ↔ Project	Student / Course / Enrollment	Object Types / Student_Obj table

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