Chapter 5 – System Design (Software) & Pre-Production (Multimedia)

🖥️ Chapter 5 – System Design (Software Development)

1) General Architecture

The system architecture shows how major components communicate: a mobile client connects to the backend over the Internet; the server handles business logic and integrates with Firebase (real-time features, messaging), APNS (iOS push), and a relational database (e.g., PostgreSQL/MySQL) for structured data.

Mobile Client: iOS/Android app handling UI, local validation, and API calls.
Server (API Layer): Authentication, authorization, business logic, integration gateways.
Firebase: Realtime DB / Cloud Messaging for certain features.
APNS: Push notifications for iOS clients.
Database: Persistent storage for users, orders, products, etc.

2) Sequence Diagrams

For each key use case, a sequence diagram clarifies component interactions over time. Example below for Place an Order:

App sends checkout request to API.
Server validates cart & user, reserves stock, calls payment gateway.
Server persists order, publishes realtime event (optional Firebase), returns confirmation.
APNS pushes status notification to the user’s device (if enabled).

3) Database Analysis & ER Diagram

The ER diagram defines entities and relationships. Tables should document primary keys, foreign keys, uniqueness, and column types.

Users

Column	Type	PK	FK	Unique	Notes
user_id	INT	✔	–	✔	Auto-increment
email	VARCHAR(255)	–	–	✔	Login identifier
password_hash	VARCHAR(255)	–	–	–	BCrypt/Argon2
role	ENUM('customer','admin')	–	–	–	Access level
created_at	TIMESTAMP	–	–	–	Default now()

Orders

Column	Type	PK	FK	Unique	Notes
order_id	INT	✔	–	✔	Auto-increment
user_id	INT	–	✔ → Users.user_id	–	Owner
total_price	DECIMAL(10,2)	–	–	–	Sum of items
status	ENUM('pending','paid','shipped','cancelled')	–	–	–	Lifecycle
created_at	TIMESTAMP	–	–	–	Default now()

Add more tables as needed (Products, OrderItems, Payments, etc.).

4) API Analysis

For each endpoint, specify method, URL, headers, body, response, and error cases.

Endpoint: POST /api/orders

Headers	`Authorization: Bearer <token>` `Content-Type: application/json`
Body	`{ "user_id": 101, "items": [ { "product_id": 20, "quantity": 2 }, { "product_id": 55, "quantity": 1 } ] }`
Response (200)	`{ "order_id": 999, "status": "pending", "created_at": "2025-08-16T09:00:00Z" }`
Errors	`400 Bad Request` – invalid or missing fields `401 Unauthorized` – invalid/expired token `409 Conflict` – stock issue `500 Internal Server Error` – unexpected failure