Types of Attributes

• Simple Attributes
• Composite Attributes
• Single-Valued Attributes
• Multi-Valued Attributes
• Stored Attributes
• Derived Attributes
• Key Attribute

Simple Attributes

Simple attributes are atomic values that cannot be divided further.

⇒ Example: A student's mobile number (10 digits), Birth Date (date-month-year).

Composite Attributes

Composite attributes consist of more than one simple attribute and can be divided into a tree-like structure.

Example: A student's complete name may have First_Name and Last_Name.

An address may include Street, City, State, Country, and PIN code.

Single-Valued Attributes

Single-valued attributes contain a single value.

Example: Aadhar_card_no, Roll_no.

Multi-Valued Attributes

Multi-valued attributes may contain more than one value and are represented by a double ellipse.

Example: A person can have more than one Phone_Number, Email_Address.

Stored Attributes

Stored attributes are physically stored in the database. Most attributes are stored except a few.

Example: Roll_No, Name, Birth_Date, Phone_No.

Derived Attributes

Derived attributes are not stored in the physical database but are derived from other attributes. Derived attributes are depicted by a dashed ellipse.

Example: Age can be derived from Birth Date.

Average Salary in a department can be derived rather than stored.

Key Attribute

A key attribute uniquely identifies each entity in the entity set. It represents a primary key and is represented by an ellipse with an underline.

Example: Roll_No will be unique for each student.

Example: ER Diagram of Student Entity Type

⇒ Student: (Roll_No, Name, BirthDate, Age, Address, Phone_Number)