Mastering Database Management

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Relational Models

Types of Attributes

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Entities are represented by means of their properties, called attributes. All attributes have values. For example, a student entity may have name, class, and age as attributes.

Attributes are the properties of entities. Attributes are represented by means of ellipses. Every ellipse represents one attribute and is directly connected to its entity (rectangle).

Types of Attributes

1. Simple Attribute −

Simple attributes are atomic values, which cannot be divided further. For example, a student’s phone number is an atomic value of 10 digits.

2.Composite attribute

Composite attributes are made of more than one simple attribute. For example, a student’s complete name may have first_name and last_name.

 3.Derived attribute −

Derived attributes are the attributes that do not exist in the physical database, but their values are derived from other attributes present in the database. For example, average_salary in a department should not be saved directly in the database, instead it can be derived. For another example, age can be derived from data_of_birth.

4.Single-Value attribute

Single-value attributes contain single value. For example − Social_Security_Number.

5.Multi-value attribute

Multi-value attributes may contain more than one values. For example, a person can have more than one phone number, email_address, etc.