ASRJC 2025 H2 Computing Prelim Paper 1 Solutions

1 A software developing company needs software to calculate how much each employee should be paid. [3] Ans 1 mark per row Rules Conditions Public holiday Y Y Y Y N N N N Hours >= 160 Y Y N N Y Y N N Pension Y N Y N Y N Y N Actions 3% bonus payment X X X X 5% bonus payment X X X X 4% pension payment X X X X (b) Explain the changes in the decision table after removing redundancies. [1] Ans: No pair of actions for a several combinations are the same. so no combinations can be combined, and no reducing the number of rules (1) (c) The company has decided to implement a program for the software using object-oriented programming (OOP). • the superclass • any subclasses • inheritance • properties • appropriate methods Ans: • inheritance (arrow filled or unfilled) (1) • 3 class names (1) • Private attributes (2) • Public methods (2) • Accessors/Getters (2) • Mutators/Setters (2) (1) (1) (1) ApprenticeshipEmployee Private: HourlyRate : REAL HoursThisWeek : REAL/INTEGER Public: Constructor() SetHoursThisWeek() GetHourlyRate() GetHoursThisWeek() SetHourlyRate() SalaryEmployee Private: MonthlyPayment : REAL HoursThisMonth: REAL PublicHoliday : BOOLEAN Pension : BOOLEAN Public: Constructor() GetMonthlyPayment() GetHoursThisMonth() GetPublicHoliday() GetPension() SetMonthlyPayment() SetHoursThisMonth() SetPublicHoliday() SetPension() Employee Private: EmployeeID : STRING Name : STRING Address : STRING DateOfBirth : Date Public: Constructor() GetEmployeeID() GetName() GetAddress() GetDateOfBirth() SetEmployeeID() SetName() SetAddress() SetDateOfBirth()

(d) A SalaryEmployee is paid a fixed monthly payment. Copy and complete the flowchart below for the function CalculateSalary(). [6] Ans: (1) mark per bullet point to max 6 • MonthlyPayment accessed from the parameter using Get method and store in BasicSalary • Hours, Pension and PublicHoliday accessed from the parameter using Get methods • Checking if Hours is > = 160, calculating bonus payment (BasicSalary * 0.05) • Checking if pension is true, calculation pension to pay (BasicSalary * 0.04) • Checking if public holiday is true, calculation of bonus payment (BasicSalary * 0.03) • Adding both bonus payments to basic salary and deducting pension from salary • Returning the new salary Start CalculateSalary(TheEmployee: SalaryEmployee) BasicSalary ← 0 BonusPayment ← 0 PensionPayment ← 0 HoursBonus ← 0.05 HoursMonthBonus ← 160 PensionCost ← 0.04 PublicHolidayBonus ← 0.03 BasicSalary ← TheEmployee.GetMonthlyPayment() (1) (1) TheEmployee.GetHoursThisMonth() >= HoursMonthBonus BonusPayment ← BasicSalary * HoursBonus TheEmployee.GetPension() = TRUE PensionPayment ← BasicSalary * PensionCost (1) TheEmployee.GetPublicHoliday() = TRUE BonusPayment ← BonusPayment + BasicSalary * PublicHolidayBonus MonthlySalary ← BasicSalary + BonusPayment – PensionPayment (1) (1) RETURN MonthlySalary End (1)

(e) (i) In OOP, state the purpose of polymorphism. [1] Ans: Allows objects or methods to exhibit different behaviors under different classes. (1) (ii) What changes in design needs to be made if the objects of class ApprenticeshipEmployee also use CalculateSalary() to calculate the weekly salary. [1] Ans: CalculateSalary() must be a public method of ApprenticeshipEmployee (1) (f) Discuss the advantages of using modular design in software development. [2] Ans: Advantages including easier maintenance and debugging, enhanced reusability of components, improved collaboration, increased scalability, faster development cycles, and better fault isolation. (2) (g) The software design may need to change from time to time by a team of programmers. Explain how the team tracks the changes with a system. [2] Ans: Version control is a system that tracks changes to files, typically code in software development, allowing teams to collaborate effectively and revert to previous versions when needed (2)

2 A company has a website. Users use the internet and the world wide web to access the website. (a) Describe the difference between the internet and the world wide web. [1] Ans: (1) The internet is the infrastructure The world wide web is a collection of web pages (b) Data packets are transmitted across a network from one computer to another computer. Describe the structure of a data packet. [1] Ans: All three from: (1) A packet is split into three different sections … the header … the payload … the trailer (c) Explain what is meant by the term router and describe the function of a router in a computer network. [2] Ans: A router is a device in a network which holds information about the addresses of computers in the network (or other networks) … (1) Any one of the function of a router (1) … and can direct data to the correct computer … and can direct data around network in (most) efficient way … and act as a gateway connecting to a larger network. (d) Explain what is meant by circuit switching and packet switching in a computer network and give two advantages of packet switching over circuit switching. [4] Ans: Circuit switching: (1) Path is set up between the sender and receiver All data follows the same path, in order Path cannot be used by any other data Packet switching: Any 2 of for one mark total: (1) Data split into packets Each packet may be transmitted by different routes Packets may arrive out of order and are re-assembled Packet switch preferred: any 2 of for one mark each (1+1) Better security as it is very difficult to intercept Makes more efficient use of data lines as there is no waiting during gaps Less likely to be affected by network failure because multiple paths used (e) A website of a company may collect information of the customers. (i) State the meaning of privacy of data. [1] Ans: (1) mark for: Either • Ensuring data can only be accessed by / disclosed to authorised persons Or • Ensuring data cannot be accessed by / disclosed to unauthorised persons (ii) State the meaning of integrity of data. [1] Ans: (1) mark for each bullet point (max 1) • Ensuring the accuracy / completeness / consistency of data (during / after processing) • Ensuring the data is up to date

(iii) Describe the following threats to a computer system. [4] Spyware Phishing email Ans: (1) mark for each bullet point. Phishing email (max 2) • The email pretends to be from an official body • ... persuading individuals to disclose private information // by example such as bank details • ... or requesting authentication by redirecting to an unofficial/unauthorised website // inviting a user to click a link Spyware (max 2) • Malware downloaded without the user’s knowledge • ... which secretly records the user’s actions / keystrokes on the computer • ... and sends logs of the actions to a third party 3 Details of errors generated in a program are stored in a stack. (a) State which error will be the first retrieved from the stack. [1] Ans: The last one in // most recent (b) The stack is implemented as a 1D array with the identifier ErrorArray. (i) The function, AddItemToStack, takes the next error, the array, and pointer as parameters. If the stack is full, the function returns FALSE; otherwise, it adds the error to the stack, changes the pointer’s value and returns TRUE. Copy and complete the following pseudocode for the function AddItemToStack. [4] Ans: 1 mark for True and False in the correct place 1 for each