Entities 'Client', 'Order', 'Product', and 'Payment'. Describe the data structure, relationships between entities, and justify the choice of storage model.

For entities "Customer", "Order", "Product", and "Payment", the following data structure and relationships can be proposed:

• Customer — the main entity, contains information about the buyer (ID, name, contacts).
• Order — linked to one Customer (one-to-many), contains order data (ID, date, status).
• Product — describes the product (ID, name, price, description).
• Payment — linked to one Order (one-to-one or one-to-many if partial payment), contains information about the amount, date, and payment method.

Relationships:

• Customer 1:N Order
• Order N:M Product (through an intermediate table "Order Items" with quantity and price)
• Order 1:N Payment

Choice of storage model:

• Relational database (e.g., PostgreSQL) is suitable for such data, as it models relationships between entities well, ensures data integrity, and supports complex queries.

• Using normalization of data helps avoid duplication and simplifies updating information.

• An intermediate table for Order-Product relationship allows storing the quantity of each product in the order and the price at the time of purchase.

Example tables:

• clients(id PK, name, contact_info)
• orders(id PK, client_id FK, order_date, status)
• products(id PK, name, price, description)
• order_items(order_id FK, product_id FK, quantity, price)
• payments(id PK, order_id FK, amount, payment_date, method)

This approach provides flexibility, scalability, and ease of working with data.