There are 3 entities - user, chat, message • The user has a name and registration date • The chat has a name and creation date • The message has text, an author, and a creation date • A user can be part of multiple chats simultaneously • A message must belong to a chat, and a message cannot belong to more than 1 chat at the same time • The domain should be described in the form of tables

To describe a domain with three entities — user, chat, message — and their relationships, you can use the following tables:

-- Users table
CREATE TABLE users (
    id SERIAL PRIMARY KEY,
    name VARCHAR(255) NOT NULL,
    registration_date DATE NOT NULL
);

-- Chats table
CREATE TABLE chats (
    id SERIAL PRIMARY KEY,
    title VARCHAR(255) NOT NULL,
    creation_date DATE NOT NULL
);

-- Messages table
CREATE TABLE messages (
    id SERIAL PRIMARY KEY,
    chat_id INT NOT NULL REFERENCES chats(id),
    author_id INT NOT NULL REFERENCES users(id),
    text TEXT NOT NULL,
    creation_date TIMESTAMP NOT NULL
);

-- User-chats relationship table (many-to-many)
CREATE TABLE user_chats (
    user_id INT NOT NULL REFERENCES users(id),
    chat_id INT NOT NULL REFERENCES chats(id),
    PRIMARY KEY (user_id, chat_id)
);

Explanation:

• A user can be part of multiple chats, so a user_chats table is needed for the many-to-many relationship.
• A message belongs to one chat and one author, so the messages table has foreign keys chat_id and author_id.
• Registration dates, chat creation dates, and message creation dates are stored in the respective fields.