Domain, Entity, Referential Integrity, and Atomic Values

Relational integrity is a broad way to discuss data correctness in relational databases. The standard terms usually include domain integrity, entity integrity, and referential integrity. Atomic values are closely related because they describe how values should be stored inside table cells.

Overview

Term	Question it answers	Typical SQL mechanism
Domain integrity	Is this column value valid?	Data type, NOT NULL, CHECK
Entity integrity	Can this row be uniquely identified?	PRIMARY KEY
Referential integrity	Does this relationship point to a valid row?	FOREIGN KEY
Atomic value	Does this cell hold one indivisible value?	Schema design

Domain integrity

Domain integrity means values in a column must belong to the allowed domain for that column.

The domain can include type, length, range, format, allowed set, and nullability.

CREATE TABLE products (
    id INT PRIMARY KEY,
    name VARCHAR(100) NOT NULL,
    price DECIMAL(10, 2) NOT NULL CHECK (price >= 0)
)

In this example, price must be a decimal value, must not be null, and must be greater than or equal to zero.

Entity integrity

Entity integrity means each row should be uniquely identifiable.

This is usually enforced with a primary key. A primary key should be unique and not null.

CREATE TABLE users (
    id INT PRIMARY KEY,
    email VARCHAR(255) NOT NULL UNIQUE
)

Referential integrity

Referential integrity means relationships between tables should stay valid.

A foreign key should point to an existing referenced row, unless the relationship is optional and null is allowed.

CREATE TABLE orders (
    id INT PRIMARY KEY,
    user_id INT NOT NULL,
    FOREIGN KEY (user_id) REFERENCES users(id)
)

Atomic value

An atomic value is a single indivisible value stored in one cell.

For relational design, a cell should not contain a list of separate values that need to be independently searched, joined, counted, or constrained.

Design	Example	Issue
Non-atomic	phone_numbers = '111,222,333'	Individual phone numbers are hidden inside one string
Atomic	one phone number per row	Each phone number can be queried and constrained

Atomic value example

CREATE TABLE user_phone_numbers (
    id INT PRIMARY KEY,
    user_id INT NOT NULL,
    phone_number VARCHAR(50) NOT NULL,
    FOREIGN KEY (user_id) REFERENCES users(id)
)

Common confusion

Relational integrity is a broad phrase. Referential integrity is the specific foreign key relationship rule.
Domain integrity is not only about data type. It also includes allowed values and constraints.
Entity integrity is about row identity, not business correctness by itself.
Atomic does not mean short. It means the value should not be split into separate meaningful values for that design.