HCI 2025 H2 Computing Prelim Paper 1 Solution

Page 1 of 15 HWA CHONG INSTITUTION C2 PRELIMINARY EXAMINATION 2025 COMPUTING Higher 2 15 Sept 2025 Paper 1 (9569 / 01) 1400 -- 1700 hrs READ THESE INSTRUCTIONS FIRST An answer booklet will be provided with this question paper. You should follow the instructions on the front cover of the answer booklet. If you need additional answer paper ask the invigilator for a continuation booklet. Answer ALL questions. Approved calculators are allowed. The number of marks is given in brackets [ ] at the end of each question or part question. The total number of marks for this paper is 100. This document consists of 6 printed pages.

Page 2 of 15 1 (a) Describe the purpose of Internet Protocol (IP) and state the format of an IPv4 address. [2] (b) Describe one disadvantage of packet switching and how the problem can be handled. [2] (c) Explain the term Domain Name Server (DNS) and how it works. [5] Soln (a) IP is responsible for routing packets of data towards their destination. IPV4 address is 32 bits or 4 groups of denary numbers between 0 and 255, separated by dots when written in dotted-decimal notation. (b) It requires more time for reassembly at the destination device as packets may arrive in random order. To handle this, a sequential number is attached to each packet, and efficient algorithms are used to sort the packets into the original order. (c) DNS server translates domain name in human language to IP addresses in machine language. DNS server first checks if the requested domain name is available in its cache. If not found in its cache, it sends requests to the local DNS by the Internet Service Provider. If still not found, DNS searches from a hierarchy of distributed database to locate the domain name. Once found, DNS server sends the IP address back to the user. 2 (a) An airline website is designed for customers to book air tickets. (i) State the purpose of data validation and give one example of how the website implements it on the customers’ date of birth. [2] (ii) State the purpose of data verification and give one example of how the website implements it on the bookings. [2] (iii) Describe two differences between a web application and a native application. [2] (b) Give two purposes of using digital signature and describe how it works. [8] (c) Describe how a firewall protects computer networks and one limitation of a firewall. [2]

Page 3 of 15 Soln (a) (i) ensure that the data entered is sensible and reasonable • Range check: year < 2026. • Format check: all digits, e.g. yyyymmdd • Length check: 8 characters, e.g. yyymmdd, • Presence check: not left blank (ii) ensure the data entered matches the original resource. Proofread of customers’ data entered before submission. (iii) Web Applications Native Applications Deployment and maintenance (updates) for a web-based application require deployment on a single set of server machines. Deployment and any maintenance/patch are done on individual client machines separately. Web applications can be accessed from anywhere (most locations), so there is no location constraint. As desktop are confined to a standalone machine, so they can be only accessed from the machines they are deployed in. Web applications are platform-independent, they can work in different types of platforms with the only requirement of a web browser. Desktop applications need to be developed separately for different platform machines. (Windows, Linux, Unix, Mac etc) Web applications are at higher security risks as they are inherently designed to increase accessibility. Desktop applications, on the other hand, have better authorization and administrators have better control, hence more secure. Web applications rely heavily on internet connectivity, for their operation. Desktop applications don’t require the internet for their operations. Some applications just require internet connectivity at the time of update. (b) purpose: • Authentication: the message was created by the known sender • Non-repudiation: the sender cannot deny having sent the message • Integrity: the message is not altered in transit Process: • The sender uses a hash algorithm to create a hashed version of the message • The sender uses its private key to encrypt the hash to the digital signature • Both the message (encrypted or not) and the digital signature are sent to the receiver • The receiver uses the sender’s public key to decrypt the digital signature back to the sender’s version of hash • The receiver uses the same hash algorithm to create a new hash from the received message • If the two hashes match, it means the data is not altered and is sent by the known sender

Page 4 of 15 (c) Firewall monitors and controls all incoming and outgoing network traffic based on a set of security rules to prevent unauthorized access from entering a private network. Limitations: Hackers can bypass firewall by inserting malicious attacks inside legitimate programs, for example, emails Firewall cannot protect against internal attacks, for example, virus in one computer in the network The setting of firewall may block some legitimate programs 3 A system processes user input and performs encoding and validation using character and number representations. (a) The ASCII code (in denary) for the character 'A' is 65. (i) Express 'D' in 7-bit binary. [1] (ii) Express 'D' as a hexadecimal value. [1] (iii) State the range of values that are common to both ASCII and Unicode. [1] (b) A user inputs the number 365, which must be stored in a 7-bit binary format. Explain the problem, and how this could be resolved. [2] (c) Give one example of a software or platform that relies on Unicode and explain its benefit in that context. [2] Soln (i) 1000100 (ii) 44 (iii) Values 0 to 127 (b) The maximum value for 7-bit unsigned binary is 127. 365 exceeds this and needs 9-bits, so it cannot be stored. This can be resolved by using a larger data type, such as 16-bit binary format. (c) Example: WhatsApp or Chrome. Unicode allows the app to support messages in multiple languages and emojis globally.

Page 5 of 15 4 A collectible toy store sells Libaba figurines that come in many series. Each series is released in a different year, and within a series release, multiple toy figurines may be produced. The following unnormalised table is used to track sales of these toys: LibabaSale SaleID SaleDate ToyID ToyName SeriesName ReleaseYear NumSold S101 1/4/2025 T001 Polar Pixie Starborn 2024 1 T002 Misty Mewling Fairytails 2025 3 S102 3/4/2025 T003 Nutty Nimlet Arborealis 2023 1 S103 5/4/2025 T002 Misty Mewling Fairytails 2025 2 T004 Jungle Jinx Arborealis 2023 2 (a) State one data redundancy and one anomaly issue present in the LibabaSale table above. [2] (b) Identify one transitive dependency that exist in the table. [2] (c) Normalise the LibabaSales table into Third Normal Form (3NF) and draw the Entity-Relationship (E -R) diagram showing the relationships between the resulting tables. [3] (d) A table description can be expressed as: TableName (Attribute1, Attribute2, Attribute3, ...) The primary key is indicated by underlining one or more attributes. Foreign keys are indicated by using a dashed underline. Write table descriptions for the tables obtained from part (c). [4] (e) Write an SQL query to display each SeriesName and the total number of Libaba sold, grouped by series and ordered from highest to lowest total. [6] (f) Explain one advantage and one disadvantage of