← QCE Digital Solutions Unit 3

The user interface as part of a system model

The part of a system where the user gives inputs and receives outputs. On a conceptual model it sits on the system boundary as the link between the user and the system.

Part of: QCE Digital Solutions Unit 3 — Innovative Digital Solutions — Module 7

Understanding The user interface as part of a system model in QCE Digital Solutions Unit 3

What it does: The interface is drawn on the boundary, in between the user and the inside of the system, so it links the two. The results are passed out to the interface, which displays them to the user as an output such as a report on screen. Storage belongs to the data store. The user interface is the point of contact where the user gives inputs and sees outputs. Tapping Submit is the user giving the system an input. An error message is an output from the system to the user.

Common mistakes: A function header must end with a colon. It should be def show_menu():. The interface takes the user's input with input(), not print(). print() only shows output. It should be user = input('Username: ').

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This module's key terms are also in a printable crossword (Modules 251–337) and word search (Modules 194–337).

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Learning
Duo
On a conceptual model, where is the user interface placed?
On the system boundary, linking the user and the systemOutside the model, because it is not part of the system
Matches
[User] → [Database] (no interface drawn)
↓
The user is linked straight to the database. The interface should be drawn on the boundary between them, as the link the user inputs and outputs pass through.
Applying
Meanings
Term
user interface
Meaning
The part of a system where the user gives inputs and receives outputs. On a conceptual model it sits on the system boundary as the link between the user and the system.
Practice
User -> User Interface: inputs
Testing
Gaps
Input: User -> -> System
Check Answer
Spots
1def show_menu()
2 print('1. Check balance')

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Quick Questions

1. On a conceptual model, where is the user interface placed?
A. Outside the model, because it is not part of the system
B. On the system boundary, linking the user and the system ✓
The user interface is the link between the user and the system, so it sits on the boundary where inputs enter and outputs leave.
2. Which describes the role of the user interface in a system?
A. Where the user gives inputs and receives outputs ✓
B. Where the database stores data permanently
Storage belongs to the data store. The user interface is the point of contact where the user gives inputs and sees outputs.
3. A student types their username and password into a login screen. What is this?
A. A user input passing through the interface ✓
B. A system output passing through the interface
Data entering the system from the user is an input. It enters the system via the interface.
4. A mobile app shows an order confirmation message on screen. What is this?
A. A system output shown to the user ✓
B. A user input given to the system
The system sends information to the user, so it is an output. The interface displays it.
5. Which is an example of the user interface in a conceptual model for a school canteen app?
A. The server hardware that runs the app in the background
B. The ordering screen where students pick items and see their total ✓
The ordering screen is where the user and the system meet. Server hardware is part of the system, not the interface.

Match the Pairs

user interface → The part of the system where the user gives inputs and receives outputs
User → Interface → Processing → A user input travelling through the interface into the system
The interface sits on the system boundary as the link between the user and the system → [User] <-> |Interface| <-> [System processing]
Outputs from the system are shown to the user through the interface → System processing → Interface → User (report on screen)
[User] → [Database] (no interface drawn) → The user is linked straight to the database. The interface should be drawn on the boundary between them, as the link the user inputs and outputs pass through.
Interface → User: "Enter username" (labelled as an input) → A prompt displayed to the user is a system output, not a user input. Inputs go from the user into the interface, such as typing a username.

Key Term

user interface
The part of a system where the user gives inputs and receives outputs. On a conceptual model it sits on the system boundary as the link between the user and the system.

Fill in the Blanks

1. Input: User -> Interface -> System
Hint: Type the system component that sits between the user and the system and passes the user's inputs in.
2. name = input("Enter your name: ")
Hint: Type the built-in function that collects a user input through the interface.
3. print("Total: " + str(total))
Hint: Type the function that shows a system output to the user.
4. # The interface sits on the system boundary
Hint: Type the word for the edge of the system where it meets its environment and the user.
5. Output: System -> Interface -> User
Hint: Type the entity outside the system that receives outputs from the interface.

Spot the Error

Question 1
A def show_menu()
B print('1. Check balance')
C choice = input('Choose: ')
D return choice
Line A — A function header must end with a colon. It should be def show_menu():
Question 2
A def login_screen():
B user = print('Username: ')
C print('Welcome,', user)
D return user
Line B — The interface takes the user's input with input(), not print(). print() only shows output. It should be user = input('Username: ').
Question 3
A def ui_output(score):
B msg = 'Your score: '
C print(msg + score)
Line C — A string cannot be joined to a number. The score must be converted first, so it should be print(msg + str(score)).
Question 4
A ui_inputs = ['username', 'pin']
B ui_outputs = ['pin', 'balance']
C print(ui_inputs, ui_outputs)
Line B — A PIN is typed in by the user, so it is an input. It is not an output shown to the user. The outputs list should hold items such as 'balance' and 'error'.
Question 5
A def atm_ui():
B pin = input('PIN: ')
C amount = input('Amount: ')
D if pin = '1234':
E print('Cash:', amount)
Line D — A single = assigns a value. A condition needs == to compare. It should be if pin == '1234':

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