Explain the importance of relationships in a relational database system. Describe the type of relationships commonly used in database design, and provide examples of how they are implemented in MS-Access.

In a relational database, a relationship links two tables via common field (primary key → foreign key). Terminology consistent across papers.

Importance:

1. Removes duplication — Citizen stored once in Citizen table, reused by ID in Service table.
2. Enforces integrity — Referential integrity blocks orphan rows (service for non-existent citizen rejected).
3. Enables queries — Joins answer "list services with citizen names" in seconds via SELECT.

Types with MS-Access implementation (Database Tools → Relationships → drag field → Enforce Integrity):

1. One-to-Many (1:M) — One Department has many Employees. Department.DeptID (PK) → Employee.DeptID (FK). Most common.
2. Many-to-Many (M:N) — Students ↔ Courses via junction Enrollment(StudentID, CourseID) split into two 1:M links.
3. One-to-One (1:1) — Employee ↔ EmployeeConfidential (PK-to-PK) to isolate sensitive data with stricter access.