What requirements are included in the functional specifications?

Functional specifications describe the behavior of the system, defining what the system should do to meet user needs. Main elements:

• Functionality description: A detailed account of each function or capability of the system. Includes input data, processing steps, and expected output.
• User requirements: Descriptions of what users expect from the system in terms of tasks performed.
• User stories: Format "As <role>, I want <action> to <goal>". Help understand user needs from their perspective.
• Use cases: Describe user interactions with the system to achieve specific goals. Include main flow and alternative scenarios.
• Data processing rules: Describe data handling logic, including validation, transformation, and storage.
• Interfaces: Describe interactions between the system and external systems or users (e.g., API, UI).
• Performance requirements (partial): May include response time requirements for critical operations. Non-functional requirements more fully describe performance.
• Security requirements (partial): May include authentication and authorization requirements for accessing certain functions. Non-functional requirements more fully describe security.
• Reports and analytics: Describe types of reports and analytical information the system should provide.
• Execution conditions: Describe conditions under which certain functions should be executed.

Example of a functionality description:

{
  "function_name": "Create a new user",
  "description": "Allows the system administrator to add a new user to the database.",
  "input_data": {
    "username": "String, unique username",
    "email": "String, unique email address",
    "password": "String, at least 8 characters",
    "role": "Enumeration (Admin, User, Guest)"
  },
  "processing_logic": [
    "Validate input data (uniqueness of username and email, password complexity, valid role value)",
    "Hash the password",
    "Save user data in the 'users' table",
    "Send notification to the new user (optional)"
  ],
  "expected_output": {
    "success": "true/false",
    "user_id": "Identifier of the created user (on success)",
    "error_message": "Error description (on failure)"
  },
  "preconditions": "User must have 'Admin' role",
  "postconditions": "A new record is created in the 'users' table in the database"
}