What is a relation schema in DBMS?

Relation Schema in DBMS

In Database Management Systems (DBMS), a relation schema defines the structure of a relation (table) in a relational database. It specifies:

• Relation name (table name)
• Attributes (columns/fields)
• Domain (data types) of attributes
• Constraints (like primary keys, foreign keys, etc.)

1️⃣ Relation Schema Definition

A relation schema is typically represented as:

R(A1,A2,A3,…,An)R(A_1, A_2, A_3, …, A_n)R(A1​,A2​,A3​,…,An​)Where:

• R → Name of the relation (table)
• A₁, A₂, A₃, …, Aₙ → Attributes (columns of the table)

Each attribute has a domain, which defines the type of values it can store.

2️⃣ Example of Relation Schema

Consider a Student table:

Student(StudentID,Name,Age,Major)Student( Student_ID, Name, Age, Major )Student(StudentI​D,Name,Age,Major)

• Relation Name: Student
• Attributes: Student_ID, Name, Age, Major
• Domains:
  • Student_ID → Integer (Unique Identifier)
  • Name → String
  • Age → Integer
  • Major → String

Corresponding Table (Relation)

3️⃣ Components of Relation Schema

(a) Attributes and Domains

Each attribute has a domain, which defines the type of values it can take.
Example:

• Student_ID → Integer
• Name → Varchar(50)
• Age → Integer
• Major → Varchar(30)

(b) Constraints in Relation Schema

1. Primary Key → Uniquely identifies each row (e.g., Student_ID)
2. Foreign Key → Establishes a relationship with another table
3. Not Null → Ensures a field cannot have NULL values
4. Unique → Ensures values in a column are unique
5. Check → Restricts values (e.g., Age > 18)

Example with Constraints (SQL Representation):

4️⃣ Difference Between Relation and Relation Schema

5️⃣ Key Takeaways

✔ Relation Schema → Defines table structure
✔ Attributes & Domains → Specify columns and their data types
✔ Constraints → Ensure data integrity (PK, FK, NOT NULL, etc.)
✔ Relation (Table) ≠ Relation Schema → One is the blueprint, the other is the actual data