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Worked solutions

IB Computer Science SL · Paper 2

Computer Science, Standard Level

Session: May 2024
Marks: 180
Duration: 1 hour
Calculator: Not allowed
Questions: 13

Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q10 Q11 Q12 Q13

Keep your copy of the paper open alongside. We don't reproduce the questions: each part below is labelled to match the May 2024 Global paper, which your school or the IB can provide.

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Option A: Databases · Option

Questions 1–3 · 45 marks

Question 1

16 marks

Sand dune ecological survey database, data types, validation, ERD, composite keys, and SQL

Databases

(a)(i)

1 mark

`String` / `Text` (or `VARCHAR` / `Alphanumeric`).

Mentor tip

Plant species names (like 'Marram grass') consist of alphabetic characters and spaces, requiring a text/string data type.

(a)(ii)

1 mark

`Real` / `Float` (or `Numeric` / `Double`, since site gradients include decimal values such as `8.2` and `7.9`).

Mentor tip

Check Figure 2 (`Site` table) where `Gradient` values are decimals like `8.2`, making `Real`/`Float` the most accurate choice.

(b)

2 marks

Apply a range check on the `Gradient` field to ensure the entered slope angle falls within a valid physical interval (for example, between `-90` and `+90` degrees, or `0` to `90` degrees).
Alternatively, apply a numeric type check to reject non-numeric characters or a presence check to ensure the field is not left blank.

- 9 0^{\circ} \leq Gradient \leq + 9 0^{\circ}

Mentor tip

Name a specific validation check (range check, type check, or presence check) and state the exact rule applied to `Gradient`.

(c)

3 marks

1. Include all three entities: `Plant`, `Distribution`, and `Site`.
2. Draw a one-to-many ( $1 : M$ ) relationship from `Plant` to `Distribution` (one plant species can be recorded across many distribution survey entries).
3. Draw a one-to-many ( $1 : M$ ) relationship from `Site` to `Distribution` (one dune site can host many plant distribution records):
`Plant (1) ----< (M) Distribution (M) >---- (1) Site`

Mentor tip

`Distribution` acts as an associative/junction table resolving the many-to-many relationship between `Plant` and `Site` into two 1-to-many relationships.

(d)

2 marks

Neither `Plant_ID` nor `Site_ID` (nor `Date`) is unique on its own in the `Distribution` table because multiple plant species grow at the same site and the same site is surveyed on multiple dates.
Combining `(Plant_ID, Site_ID, Date)` into a composite primary key uniquely identifies each survey observation without needing to add a redundant surrogate ID column.

Mentor tip

Explain both why single fields repeat in `Distribution` and how combining them uniquely identifies each row while saving storage.

(e)

4 marks

1. Identify the tables required: `Plant` and `Distribution`.
2. Join the two tables on their common key: `Plant.Plant_ID = Distribution.Plant_ID`.
3. Filter for `Plant.Species = 'Gorse'` AND `Distribution.Date = '14/10/2019'`.
4. Apply the aggregate function `COUNT(Site_ID)` to return the total number of matching sites:
`SELECT COUNT(Distribution.Site_ID) FROM Plant INNER JOIN Distribution ON Plant.Plant_ID = Distribution.Plant_ID WHERE Plant.Species = 'Gorse' AND Distribution.Date = '14/10/2019';`

Mentor tip

Ensure your query steps include the table join on `Plant_ID`, both filter conditions (`Species` and `Date`), and the `COUNT` aggregation.

(f)

3 marks

1. Enforce referential integrity constraints and cascading updates/deletes so that every `Plant_ID` and `Site_ID` foreign key in `Distribution` must correspond to an existing primary key in `Plant` and `Site`.
2. Keep the schema normalized (3NF) to eliminate duplicate data across tables, and wrap data modifications in atomic transactions with input validation rules so partial or invalid updates are rolled back.

Mentor tip

Mention referential integrity (foreign key constraints), cascading updates, normalization, and transactional atomicity/validation.

Question 2

18 marks

School bus payment transactions, concurrency locking, DBA roles, security, and database ethics

Databases

(a)

3 marks

1. Authenticate the parent's login credentials, retrieve the outstanding monthly bus fee, and initiate a database payment transaction.
2. Validate the submitted payment details; if valid and sufficient funds exist, debit the parent's payment account and credit the school transportation account.
3. Commit the transaction if all updates succeed and send a confirmation receipt to the parent; if any step fails, roll back the entire transaction so neither account is left in an inconsistent state.

Mentor tip

Trace the full lifecycle of a financial transaction: initiate -> debit/credit -> commit on success or roll back on failure.

(b)

3 marks

The DBMS applies record locking (row-level write lock) or isolation protocols as soon as the first parent begins updating the student's transportation record.
While the lock is held, the second parent's update transaction is blocked from modifying (or reading uncommitted changes to) that row until the first parent's transaction commits or rolls back and releases the lock, preventing lost updates.

Mentor tip

Explain how row/record locking (or optimistic concurrency control with write validation) guarantees mutually exclusive updates.

(c)

2 marks

1. Managing user accounts and configuring role-based access permissions.
2. Performing regular database backups, disaster recovery testing, performance tuning, and security patching.

Mentor tip

State any two standard DBA responsibilities: managing access privileges, scheduling backups/recovery, monitoring performance, or maintaining security.

(d)

4 marks

1. Role-based access controls and authentication (2 marks): Require strong unique login credentials (usernames, passwords, or multi-factor authentication) and restrict database views so parents can only view and edit their own children's records.
2. Data encryption (2 marks): Encrypt sensitive student personal and financial records both at rest on disk and in transit over the network so that intercepted data is unreadable to unauthorized parties.

Mentor tip

Focus strictly on data *security* (access control privileges, user authentication, and encryption) rather than validation/integrity.

(e)

6 marks

1. Data minimization and purpose limitation: Collect and store only student and parent information strictly required for school administration and bus transport, and delete records once students graduate.
2. Informed consent and protection of minors: Because student data involves children under 18, obtain explicit parental consent before processing data and never share or sell personal details to third parties.
3. Transparency and subject access rights: Provide parents with clear mechanisms to inspect, verify, and correct inaccuracies in their stored personal records in compliance with data protection laws.
4. Strong privacy safeguards: Implement restricted database views, redaction, encryption, and regular backups to prevent breaches or data loss.

Mentor tip

Cover privacy/encryption (especially for minors), consent/no third-party sharing, data minimization/retention limits, and parental rights to inspect and correct data.

Question 3

11 marks

Athletics records normalization, numeric data types, and constructing 2NF relations

Databases

(a)

2 marks

Normalization eliminates data redundancy (duplicate fields across rows), which reduces storage space and prevents update, insertion, and deletion anomalies, thereby maintaining data consistency.

Mentor tip

Pair reducing data redundancy/storage waste with preventing update/insert/delete anomalies.

(b)

2 marks

Values in `OlymRec` (such as `9.63` seconds or `8.90` metres) contain fractional decimal components measured to hundredths of a second or centimetre.
An integer data type only stores whole numbers and would truncate or round the fractional part, losing the precision required to distinguish athletic records.

Mentor tip

Point out that athletic times and distances require decimal precision (floating-point/real numbers), which integer types cannot store.

(c)

5 marks

1. First Normal Form (1NF): Flatten multi-valued cells so every row is atomic, and identify the composite primary key as `(Event, Gender)`.
2. Identify partial dependencies: `Type` (e.g., `Track`) and `SubType` (e.g., `Run`) depend solely on `Event` and not on `Gender`, repeating across male and female rows.
3. Decompose into two 2NF tables by moving partial dependencies into an `EVENTS` table:
• `EVENTS(Event, Type, SubType)` — Primary Key: `Event` (or surrogate `EventID`).
• `ATHLETICS(Event*, Gender, OlymRec, WldRec)` — Composite Primary Key: `(Event, Gender)`, where `Event*` is a Foreign Key referencing `EVENTS(Event)`.

Mentor tip

Clearly indicate Primary Keys and the Foreign Key (`Event*`) linking `ATHLETICS` to `EVENTS`, ensuring `Type` and `SubType` are moved to `EVENTS`.

(d)

2 marks

Databases are normalized from 2NF to 3NF to remove transitive dependencies—where a non-key attribute depends on another non-key attribute rather than directly on the primary key (for example, `SubType` determining `Type`)—further reducing redundancy and update anomalies.

Mentor tip

State that 2NF -> 3NF removes transitive (non-key to non-key) functional dependencies.

Option B: Modelling and simulation · Option

Questions 4–6 · 45 marks

Question 4

16 marks

Fitted kitchen design simulation variables, spatial rules, reliability factors, and evaluation

Modelling and simulation

(a)

3 marks

1. `WALL_WIDTH` / `WALL_HEIGHT` (or room length, width, and height dimensions).
2. `CABINET_WIDTH` / `CABINET_DEPTH` (dimensions of selected kitchen units).
3. `TILE_WIDTH` / `TILE_HEIGHT` (or sink dimensions / coordinates of plumbing fixtures).

Mentor tip

Use specific, descriptive variable names representing concrete dimensions (`WALL_WIDTH`, `CABINET_DEPTH`, `TILE_HEIGHT`) rather than vague words like 'size'.

(b)

4 marks

1. Boundary and wall-width rule (2 marks): The sum of the widths of all cabinets placed along a single wall must not exceed that wall's total width (`SUM(CABINET_WIDTH) <= WALL_WIDTH`), preventing units from overlapping or extending past corners.
2. Ergonomic clearance rule (2 marks): When cabinets or appliances are placed on opposite walls, the room width minus the combined depths of both opposing cabinets must leave sufficient walkway clearance (e.g., at least 1 metre) for a person to walk and open doors comfortably.

\sum CabinetWidth_{i} \leq WallWidth

Mentor tip

State two physical/geometric constraints and explain why each is necessary for a functional kitchen layout.

(c)

4 marks

1. Accuracy of initial room measurements (2 marks): If the customer's physical kitchen walls, angles, or window/pipe positions are measured inaccurately before input, the simulated layout will fail to fit during real-world installation.
2. Fidelity of product dimensions and colour/lighting representation (2 marks): If catalog models have slightly inaccurate cabinet dimensions or unrealistic lighting/texture colours, the installed kitchen may not fit or may disappoint the customer visually.

Mentor tip

Focus on model input accuracy (room measurements, catalog item dimensions, colour/lighting fidelity) rather than computer hardware specs.

(d)

5 marks

1. Advantages (2 marks): Customers can interactively experiment with different cabinet styles, tile patterns, and layouts before purchasing, helping prevent costly installation mistakes and improving buyer confidence.
2. Disadvantages (2 marks): Creating an accurate 3D model takes time to measure and configure, and flat screen rendering may still misrepresent real-world spatial feel or natural lighting.
3. Conclusion (1 mark): Overall, kitchen simulation is a highly valuable decision-support tool for avoiding expensive design errors, provided initial physical room measurements are exact.

Mentor tip

Include an advantage (2 marks), a disadvantage (2 marks), and a weighed conclusion (1 mark).

Question 5

10 marks

Real estate electronic brochures, 3D rendering, ray tracing, and walkthrough ethics

Modelling and simulation

(a)

2 marks

Because the brochure only contains static text and 2D photographs, standard device RAM is generally sufficient; however, if many uncompressed high-resolution photographs are loaded simultaneously, sufficient RAM is needed to buffer and display them smoothly without lag.

Mentor tip

Note that static text/photos require modest memory, though high-resolution image sets still require adequate RAM for smooth loading.

(b)

1 mark

3D rendering (or image-based 3D reconstruction / photogrammetry rendering).

Mentor tip

The standard syllabus term expected here is `(3D) rendering`.

(c)

3 marks

Ray tracing mathematically traces the path of light rays from light sources (such as windows and lamps) as they reflect, refract, and cast shadows across surfaces inside the rooms.
This allows rooms and furniture to be viewed dynamically from any camera angle or viewpoint with realistic lighting and reflections.
Consequently, potential buyers experience a much more lifelike, immersive virtual walk-through of the property.

Mentor tip

Explain how ray tracing computes light paths/reflections/shadows across viewpoints to create a realistic virtual walk-through.

(d)

4 marks

1. Homeowner privacy and physical security (2 marks): Detailed 3D walk-throughs may inadvertently capture personal family items, valuables, or the exact locations of window locks and alarm sensors, which malicious actors (burglars) could exploit to plan a break-in.
2. Misrepresentation / deceptive marketing (2 marks): Wide-angle virtual lenses, artificial lighting, or digital staging in animations may exaggerate room sizes or conceal structural defects (such as dampness or cracks), misleading prospective buyers.

Mentor tip

Provide two distinct ethical concerns (e.g., homeowner privacy/burglary security risks and buyer deception/exaggerated room quality) for 2 marks each.

Question 6

19 marks

Supermarket quarterly sales spreadsheet model, target forecasting formulas, and parallel arrays

Modelling and simulation

(a)(i)

1 mark

`=SUM(B3:E3)` (or `=B3+C3+D3+E3`).

Mentor tip

Always begin spreadsheet formulas with an equals sign `=`.

(a)(ii)

1 mark

`=AVERAGE(B3:E3)` (or `=F3/4`).

Mentor tip

Either `=AVERAGE(B3:E3)` or dividing the whole-year total by 4 (`=F3/4`) is valid.

(a)(iii)

1 mark

`=MAX(B3:E3)`

Mentor tip

Use `MAX` over the four quarterly columns `B3:E3`.

(a)(iv)

1 mark

`=MIN(B3:E3)`

Mentor tip

Use `MIN` over the four quarterly columns `B3:E3`.

(b)

5 marks

1. Store the adjustable target percentage increase `7` (or `7%`) in cell `C12` (next to the `Target increase (%)` label in row 12).
2. In cell `B16` (Bakery Apr–Jun target), enter a formula referencing `B3` and using an absolute reference to ` $C$ 12`: `=B3 * (1 + $C$ 12 / 100)` (or `=B3 * (1 + $C$ 12)` if formatted as `7%`).
3. Copy the formula across cells `C16`, `D16`, and `E16` for the remaining three quarters (`=C3*(1+ $C$ 12/100)`, `=D3*(1+ $C$ 12/100)`, `=E3*(1+ $C$ 12/100)`).
4. In cell `F16` (Whole year target), calculate `=SUM(B16:E16)` (or `=F3*(1+ $C$ 12/100)`).
5. In cell `G16` (Quarter average target), calculate `=AVERAGE(B16:E16)` (or `=F16/4`).

Target = Actual \times (1 + \frac{TargetIncrease}{100})

Mentor tip

Use an absolute cell reference (` $C$ 12`) for the 7% target cell so that copying the formula across columns B16 to G16 keeps pointing to the target percentage.

(c)

2 marks

The model in Figure 4 only tracks *unit sales volume* (in thousands of units) rather than financial prices, wholesale stock costs, utilities, or staff wages, and relies on only a single historical year (`2020–2021`) with a uniform percentage target, making it insufficient to predict actual monetary profit.

Mentor tip

Point out that relying on a single year of unit sales (or applying one flat percentage across all departments without cost/trend data) cannot accurately predict future profit.

(d)(i)

1 mark

`=B24+B28` (or `=SUM(B24, B28)` / `=B24+B26+B27`, summing Total Wholesale costs and Total Other costs).

Mentor tip

Row 30 (`Total costs`) is the sum of row 24 (`Total` wholesale costs) and row 28 (`Total` other costs).

(d)(ii)

1 mark

`=B13-B30` (Total Revenues in `B13` minus Total costs in `B30`).

Profit = Total Revenue - Total Costs

Mentor tip

Profit in `B32` equals Total Revenue (`B13`) minus Total Costs (`B30`).

(e)

6 marks

Use a loop from `0` to `7` (for the 8 departments in `DEPARTMENT[]`), prompt the user to input each of the four quarterly sales figures into parallel arrays (`APR_JUN[]`, `JUL_SEP[]`, `OCT_DEC[]`, `JAN_MAR[]`), and compute `WHOLE_YEAR[I]` as the sum of the four quarters:
```text loop I from 0 to 7 output "Enter quarterly figures for department: ", DEPARTMENT[I] output "Apr-Jun sales: " input APR_JUN[I] output "Jul-Sept sales: " input JUL_SEP[I] output "Oct-Dec sales: " input OCT_DEC[I] output "Jan-Mar sales: " input JAN_MAR[I] WHOLE_YEAR[I] = APR_JUN[I] + JUL_SEP[I] + OCT_DEC[I] + JAN_MAR[I] end loop ```

Mentor tip

Ensure you use descriptive parallel array names for all four quarters and the annual total, include clear user prompts inside the loop, and sum the four elements into `WHOLE_YEAR[I]`.

Option C: Web science · Option

Questions 7–9 · 45 marks

Question 7

20 marks

Full URLs, HTML/JavaScript DOM rendering, static pages, client-side scripting, DNS, and mobile lossy compression

Web science

(a)

2 marks

The URL `https://www.educationalsite.org/assets/home.html` is a full (absolute) URL because it specifies every component needed to locate the exact resource:
1. Protocol/Scheme (`https://`), Subdomain (`www`), Domain name (`educationalsite`), and Top-Level Domain (`org`).
2. Directory path (`/assets/`) and specific file resource name (`home.html`).

Mentor tip

Break the URL down into all its explicit parts: scheme/protocol, subdomain + domain + TLD, directory path, and filename.

(b)

3 marks

1. Above the table, display a large Level 1 heading: **Mother tongue Languages**.
2. Below the heading, draw a bordered table (`border=1`) with two rows: the top cell contains `Mother Tongue`.
3. Note the syntax bugs in the script (`var subjects = [...]:` uses a colon instead of a semicolon, and `.InnerHTML` has a capital `I` instead of `.innerHTML`), OR if interpreted as intended, the second row displays the list of 7 languages separated by line breaks (`English`, `Spanish`, `French`, `Hindi`, `Mandarin`, `Japanese`, `Korean`) — or remains blank if the script fails due to the syntax/capitalization errors:
```text Mother tongue Languages +-------------------+ | Mother Tongue | +-------------------+ | English | | Spanish | | French | | Hindi | | Mandarin | | Japanese | | Korean | +-------------------+ ```

Mentor tip

Include the `<h1>` heading above the table, the bordered top row `'Mother Tongue'`, and either the vertical list of 7 languages in the second cell or a blank second cell (noting the `.InnerHTML` / `:` script typos).

(c)

2 marks

The webpage displays the exact same hardcoded list of languages every time it is loaded, independent of user input, time of day, or external database queries.
Changing the displayed languages requires a developer to manually edit and save the HTML/JavaScript source file.

Mentor tip

Explain that content is hardcoded in the client file with no connection to an external database or server-side script, so it never changes unless the source code is edited.

(d)

3 marks

Client-side scripting languages like JavaScript execute directly inside the user's browser to provide dynamic interactivity, DOM manipulation, and input validation without reloading the page from the server.
Because JavaScript is a universal web standard used across millions of websites, browsers must support it consistently so webpages render and function identically across different devices and operating systems.

Mentor tip

Link local browser execution of JavaScript to interactive user experiences and cross-browser standardization.

(e)

2 marks

A **protocol** (such as HTTP or TCP/IP) is a strict, formal set of rules governing how data packets are formatted, transmitted, and received during network communication.
A **standard** (such as HTML5 or W3C accessibility guidelines) is an agreed-upon technical specification or framework endorsed by an organization to ensure cross-platform compatibility during development.

Mentor tip

Protocol = rules for network communication/data transmission; Standard = agreed specification/framework for compatible development.

(f)

4 marks

1. When the user enters the URL, the browser first checks its local DNS cache (and OS cache) to see if the domain name has recently been mapped to an IP address.
2. If not cached locally, the client sends a DNS lookup query at the TCP/IP application layer to a configured recursive DNS resolver (ISP DNS server).
3. If the resolver does not have the record, it queries the hierarchy of Root, Top-Level Domain (TLD, e.g., `.org`), and Authoritative name servers that hold the master directory for that domain.
4. Once the matching IP address is found, it is returned to the user's browser so it can establish a direct HTTP/TCP connection to the web server (or an error message is returned if the domain does not exist).

Mentor tip

Trace the lookup chain: local browser cache -> DNS resolver -> TLD/authoritative server -> IP address returned to browser.

(g)

4 marks

1. Smaller file size for faster wireless transfer and storage savings (2 marks): Lossy compression achieves much higher compression ratios than lossless methods, enabling video files to download rapidly over mobile cellular networks and occupy far less limited flash storage on a smartphone.
2. Imperceptible quality loss on small screens and lower data costs (2 marks): On a compact smartphone screen, minor pixel or audio artifacts discarded by lossy compression are barely noticeable to the viewer, while the reduced data transfer saves mobile data allowances and battery power.

Mentor tip

Organize your explanation around two clusters (2 marks each): File Size/Speed/Storage and Visual Quality on small mobile screens/Data Cost.

Question 8

11 marks

Keyword vs phrase searching, breadth-first web crawling, PageRank features, and black hat SEO

Web science

(a)

2 marks

Search engines match core keywords directly against indexed page `<meta>` tags, titles, and inverted index terms.
Entering a conversational question phrase (`'Did George Washington have a diary?'`) includes common stop words (`Did`, `have`, `a`) and rigid phrasing that may either be ignored or trigger false-positive matches on unrelated pages, whereas targeted keywords (`George Washington diary`) yield more precise results.

Mentor tip

Explain that keywords match indexed meta tags/content directly while conversational phrases introduce stop words or literal phrasing ambiguities.

(b)

1 mark

`A`, `B`, `E` (visiting the root `A` first, followed by its immediate level-1 children `B` and `E` from left to right before descending to level 2).

Mentor tip

Breadth-first search visits nodes level by level: Root (`A`), then its direct children (`B`, `E`, `H`, `K`) before visiting grandchildren (`C`, `D`, etc.).

(c)

2 marks

Breadth-first crawling indexes all top-level and shallow-depth pages across websites before descending into deep link chains.
This prevents the crawler from getting trapped in deep or infinite hierarchy loops on a single site and ensures high-importance homepages and main directory pages are indexed first.

Mentor tip

Highlight that breadth-first search prioritizes higher-level, more important pages across the web and avoids getting stuck down a single deep path.

(d)

2 marks

1. It calculates a numerical authority score for each webpage based on both the quantity and the PageRank weight of incoming backlinks (and outgoing link counts).
2. It is a recursive/iterative algorithm that incorporates a damping factor (typically around `0.85`) to model the probability that a random web surfer continues clicking links.

Mentor tip

State two specific PageRank properties: weighting by incoming link importance, recursive calculation, or use of a damping factor.

(e)

4 marks

1. Inaccurate historical research and compromised academic validity (2 marks): Black hat tactics like keyword stuffing (`'George Washington diary'`), hidden text, or link farms artificially push low-quality, biased, or fabricated webpages to the top of search results, causing DP History students like Brooke to cite unreliable sources in their assignments.
2. Wasted study time and security risks (2 marks): Cloak-and-redirect or bait-and-switch pages waste students' time and bandwidth visiting irrelevant commercial sites, and may expose their computers to malware or phishing.

Mentor tip

Explicitly connect the effects of black hat SEO (inaccurate sources, wasted time, malware redirects) to DP History students like Brooke to earn full marks.

Question 9

14 marks

ARPANET distributed architecture, client-server advantages, P2P vs cloud computing, and open standards

Web science

(a)

2 marks

Fault tolerance and resilience: By distributing nodes across multiple locations without a single central switch, the military network could continue routing messages along alternative paths even if several nodes or links failed or were destroyed.
It also allowed geographically dispersed research institutions to share scarce mainframe computing resources.

Mentor tip

Identify fault tolerance/redundancy (surviving node failures) or resource sharing across geographically dispersed mainframes, and expand on how it works.

(b)

2 marks

Centralized administration and security: Because data, applications, and user authentication are managed on the central mainframe server, administrators can enforce uniform security policies and backups while allowing client terminals to operate with minimal local hardware/processing power.

Mentor tip

Mention either centralized security/resource management or lightweight hardware requirements for client terminals.

(c)

4 marks

1. Cloud computing (2 marks): Resources (storage, processing, software) are hosted and managed centrally in large provider data centres and delivered over the internet as scalable services (SaaS, PaaS, IaaS) with centralized control and rapid elasticity.
2. Peer-to-Peer (P2P) computing (2 marks): Architecture is decentralized with no central server; equal peer nodes directly share their own local files, bandwidth, and processing power with one another, with access controlled by individual participants.

Mentor tip

Contrast centralized data-centre service provision (Cloud) with decentralized direct resource sharing among equal nodes (P2P).

(d)

6 marks

1. Role of open standards (3 marks): Royalty-free, publicly documented protocols and formats (such as HTTP, HTML, TCP/IP, and XML) prevent any single government or corporation from monopolizing web communication. Anyone can build a web server, browser, or site without licensing fees, empowering independent publishing and global collaboration.
2. Role of interoperability (3 marks): Built on open standards, interoperability ensures that heterogeneous hardware devices, operating systems, and databases can exchange and process data seamlessly without proprietary middlemen or custom translation layers, allowing distributed nodes worldwide to form a cohesive, decentralized web.

Mentor tip

Address both Open Standards (3 marks: HTTP/HTML/TCP-IP removing proprietary gatekeepers) and Interoperability (3 marks: seamless cross-system data exchange).

Option D: Object-oriented programming · Option

Questions 10–13 · 45 marks

Question 10

14 marks

Car rental object fundamentals, accessors and mutators, default constructors, and subclass inheritance

Object-oriented programming

(a)

2 marks

An object is a concrete runtime instance of a class that encapsulates both state (data attributes/properties) and behaviour (methods/actions that operate on that data) within an allocated block of memory.

Mentor tip

Mention that an object is an instance of a class combining data attributes (state) and methods (behaviour).

(b)

1 mark

`setPricePerDay(double pricePerDay)` (or `setNumberPlate`, `setBrandModel`, `setYear`, `setRentalClass`, `setFuelType`, `setTransmissionType`).

Mentor tip

Name any setter method starting with `set` followed by one of the attributes listed in the `Rental` UML diagram.

(c)

3 marks

Declare a `public` method with return type `String` and return the `brandModel` attribute:
```java public String getBrandModel() { return this.brandModel; } ```

Mentor tip

Include the `public` visibility modifier, `String` return type, empty parameter list `()`, and `return brandModel;` statement.

(d)

2 marks

A default constructor is a parameterless constructor that instantiates a new object in memory and initializes its instance variables to sensible default or `null`/`0`/`false` values.

Mentor tip

State both that it takes no parameters and that it instantiates the object with default attribute values.

(e)

2 marks

Change the data type of `fuelType` from `boolean` (which can only represent two states: petrol or diesel) to a type capable of representing four distinct fuel categories (petrol, diesel, electric, hybrid), such as `String`, `char`, or `int` ( along with updating its getter and setter).

Mentor tip

Explain that `boolean` only supports 2 values, so `fuelType` must be changed to `String`, `char`, or `int` to accommodate 4 fuel types.

(f)

1 mark

Inheritance (`Car` is a subclass/child of superclass `Rental`, or `Car` **is-a** `Rental`).

Mentor tip

State `inheritance` (or `Car is-a Rental` / `Car extends Rental`).

(g)

3 marks

Use `extends Rental` to inherit existing attributes/methods, declare `private int numberOfDoors`, initialize it to `4` in the default constructor (calling `super()`), and provide its accessor/mutator:
```java public class Car extends Rental { private int numberOfDoors; public Car() { super(); this.numberOfDoors = 4; } public int getNumberOfDoors() { return this.numberOfDoors; } public void setNumberOfDoors(int n) { this.numberOfDoors = n; } } ```

Mentor tip

Include `extends Rental`, `private int numberOfDoors;`, `public Car() { numberOfDoors = 4; }`, and getter/setter methods for `numberOfDoors`.

Question 11

8 marks

OOP principles (inheritance, encapsulation, polymorphism, abstraction) and modularity

Object-oriented programming

(a)

1 mark

Inheritance.

Mentor tip

Declaring `Car` as a specialized version of `Rental` (`extends Rental`) uses inheritance.

(b)

3 marks

1. Code reuse and faster development (2 marks): Common attributes (like `numberPlate` and `pricePerDay`) and methods are written and tested once in the `Rental` superclass and automatically shared by `Car`, `Bus`, and `Van` without duplicating code.
2. Easier maintenance and extensibility (1 mark): Fixing a bug or updating a method in `Rental` immediately propagates to all vehicle subclasses, and new vehicle types can be added cleanly.

Mentor tip

Explain one benefit in detail (e.g., code reuse of tested parent methods) and identify a second benefit (e.g., reduced maintenance cost or extensibility).

(c)

2 marks

1. Encapsulation.
2. Polymorphism (or Abstraction).

Mentor tip

Name any two of the remaining core OOP pillars: Encapsulation, Polymorphism, or Abstraction.

(d)

2 marks

Faster parallel development and easier debugging: Dividing a program into self-contained modules allows separate developer teams to code and test modules concurrently, and isolates bugs to smaller, manageable units of code.

Mentor tip

Choose one clear advantage of modularity (easier isolated debugging/testing, parallel team development, or code readability) and explain why it occurs.

Question 12

15 marks

Parameter variables, array deduplication in findBrandModels(), and multi-criteria filtering

Object-oriented programming

(a)

2 marks

A parameter variable is a variable declared in a method's signature (header) that receives a value or object reference passed into the method when it is called.

Mentor tip

Mention both that it is declared in the method signature/header and that it receives data (by value or reference) from the caller.

(b)

8 marks

Create a `Car[] result = new Car[100]` array and a counter `count = 0`. Loop through non-null elements of `allCars`, check if `allCars[i].getBrandModel()` already matches any car in `result[0 .. count-1]` using `.equals()`, and if not found, insert `allCars[i]` at `result[count++]`:
```java public Car[] findBrandModels(Car[] allCars) { Car[] result = new Car[100]; int count = 0; for (int i = 0; i < allCars.length && allCars[i] != null; i++) { boolean found = false; for (int j = 0; j < count; j++) { if (result[j] != null && result[j].getBrandModel().equals(allCars[i].getBrandModel())) { found = true; } } if (!found) { result[count] = allCars[i]; count++; } } return result; } ```

Mentor tip

Check every mark point: correct signature returning `Car[]`, `new Car[100]`, outer loop checking `allCars[i] != null`, resetting `boolean found = false` inside the outer loop, inner loop checking uniqueness with `.equals()`, adding when `!found`, and returning `result`.

(c)

5 marks

1. Call `findBrandModels(allCars)` first and store the returned array of unique car models in a local array (e.g., `uniqueCars`).
2. Iterate through each non-null `Car` object in `uniqueCars` using a loop.
3. For each car, use accessor methods to check if all three conditions hold: `isFuelType() == true` (petrol), `isTransmissionType() == false` (or `true`, matching automatic transmission), and `getPricePerDay() < 35.0`.
4. If a car satisfies all three criteria, copy it into a `desiredCars` array (or print its details directly); if it fails any condition, skip it (or set its slot in `uniqueCars` to `null`).
5. Output or return the filtered list of matching unique cars to the customer.

Mentor tip

Be sure to call `findBrandModels(allCars)` as your first step so the results presented to the customer contain no duplicate `brandModel` entries.

Question 13

8 marks

Customer-Car object associations, circular dependency pitfalls, and database ethics

Object-oriented programming

(a)

1 mark

Draw a directed association / aggregation arrow pointing from `Customer` to `Car` (`Customer` **has-a** reference to `Car` objects in its rental history and current rental):
`[ Customer ] --------> [ Car ]` (or `[ Customer ] <>------> [ Car ]`)

Mentor tip

Show `Customer` pointing to `Car` (indicating that a `Customer` object holds references to `Car` objects).

(b)

2 marks

Adding `customerID` inside `Rental` while `Customer` already holds references to `Car` creates a circular (bidirectional) dependency where `Customer` depends on `Car` and `Car` depends on `Customer`.
This tight coupling duplicates relationship data, increases maintenance overhead when either class changes, and risks data inconsistency if one side is updated without the other.

Mentor tip

Highlight that mutual references (`Customer` has-a `Car` and `Car` has-a `Customer`) create a circular/redundant dependency that increases coupling and inconsistency risks.

(c)

5 marks

1. Obligation to protect customer privacy: Programmers must practice data minimization by collecting only personal details strictly necessary for car rental contracts, limiting exposure of private customer lives.
2. Obligation to ensure data security: Programmers must implement strong encryption, authentication, and access controls to safeguard stored addresses, IDs, and rental histories from unauthorized breaches or misuse.
3. Obligation to maintain data accuracy and integrity: Programmers should build input validation and verification mechanisms so customer records are not corrupted or falsely attributed.

Mentor tip

Structure your answer around two clear obligations (e.g., privacy/data minimization and security/encryption or integrity/validation), giving the obligation, technical implementation, and ethical reason for each.

Our analysis

Where the marks are

Each part sorted by the topic it mostly tests. Databases carries the most marks on this paper.

Databases45 marks · 25%
Q1, Q2, Q3
Modelling and simulation45 marks · 25%
Q4, Q5, Q6
Web science45 marks · 25%
Q7, Q8, Q9
Object-oriented programming45 marks · 25%
Q10, Q11, Q12, Q13

Mentor insights

Traps to watch for

01
Databases: School bus payment transactions, concurrency locking, DBA roles, · Q2
Trace the full lifecycle of a financial transaction: initiate -> debit/credit -> commit on success or roll back on failure.
02
Modelling and simulation: Supermarket quarterly sales spreadsheet model, target forecasting · Q6
Always begin spreadsheet formulas with an equals sign `=`.
03
Web science: Full URLs, HTML/JavaScript DOM rendering, static pages, client-si · Q7
Break the URL down into all its explicit parts: scheme/protocol, subdomain + domain + TLD, directory path, and filename.
04
Object-oriented programming: Parameter variables, array deduplication in findBrandModels(), an · Q12
Mention both that it is declared in the method signature/header and that it receives data (by value or reference) from the caller.

Solutions and tips are GeorgeTheTutor's own; the questions are not reproduced here. Not affiliated with or endorsed by the International Baccalaureate Organization.

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Worked solutions

IB Computer Science SL · Paper 2

Computer Science, Standard Level

Session: May 2024
Marks: 180
Duration: 1 hour
Calculator: Not allowed
Questions: 13

Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q10 Q11 Q12 Q13

Keep your copy of the paper open alongside. We don't reproduce the questions: each part below is labelled to match the May 2024 Global paper, which your school or the IB can provide.

Practice mode

Hide our working until you've had a go.

Option A: Databases · Option

Questions 1–3 · 45 marks

Question 1

16 marks

Sand dune ecological survey database, data types, validation, ERD, composite keys, and SQL

Databases

(a)(i)

1 mark

`String` / `Text` (or `VARCHAR` / `Alphanumeric`).

Mentor tip

Plant species names (like 'Marram grass') consist of alphabetic characters and spaces, requiring a text/string data type.

(a)(ii)

1 mark

`Real` / `Float` (or `Numeric` / `Double`, since site gradients include decimal values such as `8.2` and `7.9`).

Mentor tip

Check Figure 2 (`Site` table) where `Gradient` values are decimals like `8.2`, making `Real`/`Float` the most accurate choice.

(b)

2 marks

Apply a range check on the `Gradient` field to ensure the entered slope angle falls within a valid physical interval (for example, between `-90` and `+90` degrees, or `0` to `90` degrees).
Alternatively, apply a numeric type check to reject non-numeric characters or a presence check to ensure the field is not left blank.

- 9 0^{\circ} \leq Gradient \leq + 9 0^{\circ}

Mentor tip

Name a specific validation check (range check, type check, or presence check) and state the exact rule applied to `Gradient`.

(c)

3 marks

1. Include all three entities: `Plant`, `Distribution`, and `Site`.
2. Draw a one-to-many ( $1 : M$ ) relationship from `Plant` to `Distribution` (one plant species can be recorded across many distribution survey entries).
3. Draw a one-to-many ( $1 : M$ ) relationship from `Site` to `Distribution` (one dune site can host many plant distribution records):
`Plant (1) ----< (M) Distribution (M) >---- (1) Site`

Mentor tip

`Distribution` acts as an associative/junction table resolving the many-to-many relationship between `Plant` and `Site` into two 1-to-many relationships.

(d)

2 marks

Neither `Plant_ID` nor `Site_ID` (nor `Date`) is unique on its own in the `Distribution` table because multiple plant species grow at the same site and the same site is surveyed on multiple dates.
Combining `(Plant_ID, Site_ID, Date)` into a composite primary key uniquely identifies each survey observation without needing to add a redundant surrogate ID column.

Mentor tip

Explain both why single fields repeat in `Distribution` and how combining them uniquely identifies each row while saving storage.

(e)

4 marks

1. Identify the tables required: `Plant` and `Distribution`.
2. Join the two tables on their common key: `Plant.Plant_ID = Distribution.Plant_ID`.
3. Filter for `Plant.Species = 'Gorse'` AND `Distribution.Date = '14/10/2019'`.
4. Apply the aggregate function `COUNT(Site_ID)` to return the total number of matching sites:
`SELECT COUNT(Distribution.Site_ID) FROM Plant INNER JOIN Distribution ON Plant.Plant_ID = Distribution.Plant_ID WHERE Plant.Species = 'Gorse' AND Distribution.Date = '14/10/2019';`

Mentor tip

Ensure your query steps include the table join on `Plant_ID`, both filter conditions (`Species` and `Date`), and the `COUNT` aggregation.

(f)

3 marks

1. Enforce referential integrity constraints and cascading updates/deletes so that every `Plant_ID` and `Site_ID` foreign key in `Distribution` must correspond to an existing primary key in `Plant` and `Site`.
2. Keep the schema normalized (3NF) to eliminate duplicate data across tables, and wrap data modifications in atomic transactions with input validation rules so partial or invalid updates are rolled back.

Mentor tip

Mention referential integrity (foreign key constraints), cascading updates, normalization, and transactional atomicity/validation.

Question 2

18 marks

School bus payment transactions, concurrency locking, DBA roles, security, and database ethics

Databases

(a)

3 marks

1. Authenticate the parent's login credentials, retrieve the outstanding monthly bus fee, and initiate a database payment transaction.
2. Validate the submitted payment details; if valid and sufficient funds exist, debit the parent's payment account and credit the school transportation account.
3. Commit the transaction if all updates succeed and send a confirmation receipt to the parent; if any step fails, roll back the entire transaction so neither account is left in an inconsistent state.

Mentor tip

Trace the full lifecycle of a financial transaction: initiate -> debit/credit -> commit on success or roll back on failure.

(b)

3 marks

The DBMS applies record locking (row-level write lock) or isolation protocols as soon as the first parent begins updating the student's transportation record.
While the lock is held, the second parent's update transaction is blocked from modifying (or reading uncommitted changes to) that row until the first parent's transaction commits or rolls back and releases the lock, preventing lost updates.

Mentor tip

Explain how row/record locking (or optimistic concurrency control with write validation) guarantees mutually exclusive updates.

(c)

2 marks

1. Managing user accounts and configuring role-based access permissions.
2. Performing regular database backups, disaster recovery testing, performance tuning, and security patching.

Mentor tip

State any two standard DBA responsibilities: managing access privileges, scheduling backups/recovery, monitoring performance, or maintaining security.

(d)

4 marks

1. Role-based access controls and authentication (2 marks): Require strong unique login credentials (usernames, passwords, or multi-factor authentication) and restrict database views so parents can only view and edit their own children's records.
2. Data encryption (2 marks): Encrypt sensitive student personal and financial records both at rest on disk and in transit over the network so that intercepted data is unreadable to unauthorized parties.

Mentor tip

Focus strictly on data *security* (access control privileges, user authentication, and encryption) rather than validation/integrity.

(e)

6 marks

1. Data minimization and purpose limitation: Collect and store only student and parent information strictly required for school administration and bus transport, and delete records once students graduate.
2. Informed consent and protection of minors: Because student data involves children under 18, obtain explicit parental consent before processing data and never share or sell personal details to third parties.
3. Transparency and subject access rights: Provide parents with clear mechanisms to inspect, verify, and correct inaccuracies in their stored personal records in compliance with data protection laws.
4. Strong privacy safeguards: Implement restricted database views, redaction, encryption, and regular backups to prevent breaches or data loss.

Mentor tip

Cover privacy/encryption (especially for minors), consent/no third-party sharing, data minimization/retention limits, and parental rights to inspect and correct data.

Question 3

11 marks

Athletics records normalization, numeric data types, and constructing 2NF relations

Databases

(a)

2 marks

Normalization eliminates data redundancy (duplicate fields across rows), which reduces storage space and prevents update, insertion, and deletion anomalies, thereby maintaining data consistency.

Mentor tip

Pair reducing data redundancy/storage waste with preventing update/insert/delete anomalies.

(b)

2 marks

Values in `OlymRec` (such as `9.63` seconds or `8.90` metres) contain fractional decimal components measured to hundredths of a second or centimetre.
An integer data type only stores whole numbers and would truncate or round the fractional part, losing the precision required to distinguish athletic records.

Mentor tip

Point out that athletic times and distances require decimal precision (floating-point/real numbers), which integer types cannot store.

(c)

5 marks

1. First Normal Form (1NF): Flatten multi-valued cells so every row is atomic, and identify the composite primary key as `(Event, Gender)`.
2. Identify partial dependencies: `Type` (e.g., `Track`) and `SubType` (e.g., `Run`) depend solely on `Event` and not on `Gender`, repeating across male and female rows.
3. Decompose into two 2NF tables by moving partial dependencies into an `EVENTS` table:
• `EVENTS(Event, Type, SubType)` — Primary Key: `Event` (or surrogate `EventID`).
• `ATHLETICS(Event*, Gender, OlymRec, WldRec)` — Composite Primary Key: `(Event, Gender)`, where `Event*` is a Foreign Key referencing `EVENTS(Event)`.

Mentor tip

Clearly indicate Primary Keys and the Foreign Key (`Event*`) linking `ATHLETICS` to `EVENTS`, ensuring `Type` and `SubType` are moved to `EVENTS`.

(d)

2 marks

Mentor tip

State that 2NF -> 3NF removes transitive (non-key to non-key) functional dependencies.

Option B: Modelling and simulation · Option

Questions 4–6 · 45 marks

Question 4

16 marks

Fitted kitchen design simulation variables, spatial rules, reliability factors, and evaluation

Modelling and simulation

(a)

3 marks

1. `WALL_WIDTH` / `WALL_HEIGHT` (or room length, width, and height dimensions).
2. `CABINET_WIDTH` / `CABINET_DEPTH` (dimensions of selected kitchen units).
3. `TILE_WIDTH` / `TILE_HEIGHT` (or sink dimensions / coordinates of plumbing fixtures).

Mentor tip

Use specific, descriptive variable names representing concrete dimensions (`WALL_WIDTH`, `CABINET_DEPTH`, `TILE_HEIGHT`) rather than vague words like 'size'.

(b)

4 marks

1. Boundary and wall-width rule (2 marks): The sum of the widths of all cabinets placed along a single wall must not exceed that wall's total width (`SUM(CABINET_WIDTH) <= WALL_WIDTH`), preventing units from overlapping or extending past corners.
2. Ergonomic clearance rule (2 marks): When cabinets or appliances are placed on opposite walls, the room width minus the combined depths of both opposing cabinets must leave sufficient walkway clearance (e.g., at least 1 metre) for a person to walk and open doors comfortably.

\sum CabinetWidth_{i} \leq WallWidth

Mentor tip

State two physical/geometric constraints and explain why each is necessary for a functional kitchen layout.

(c)

4 marks

1. Accuracy of initial room measurements (2 marks): If the customer's physical kitchen walls, angles, or window/pipe positions are measured inaccurately before input, the simulated layout will fail to fit during real-world installation.
2. Fidelity of product dimensions and colour/lighting representation (2 marks): If catalog models have slightly inaccurate cabinet dimensions or unrealistic lighting/texture colours, the installed kitchen may not fit or may disappoint the customer visually.

Mentor tip

Focus on model input accuracy (room measurements, catalog item dimensions, colour/lighting fidelity) rather than computer hardware specs.

(d)

5 marks

1. Advantages (2 marks): Customers can interactively experiment with different cabinet styles, tile patterns, and layouts before purchasing, helping prevent costly installation mistakes and improving buyer confidence.
2. Disadvantages (2 marks): Creating an accurate 3D model takes time to measure and configure, and flat screen rendering may still misrepresent real-world spatial feel or natural lighting.
3. Conclusion (1 mark): Overall, kitchen simulation is a highly valuable decision-support tool for avoiding expensive design errors, provided initial physical room measurements are exact.

Mentor tip

Include an advantage (2 marks), a disadvantage (2 marks), and a weighed conclusion (1 mark).

Question 5

10 marks

Real estate electronic brochures, 3D rendering, ray tracing, and walkthrough ethics

Modelling and simulation

(a)

2 marks

Mentor tip

Note that static text/photos require modest memory, though high-resolution image sets still require adequate RAM for smooth loading.

(b)

1 mark

3D rendering (or image-based 3D reconstruction / photogrammetry rendering).

Mentor tip

The standard syllabus term expected here is `(3D) rendering`.

(c)

3 marks

Ray tracing mathematically traces the path of light rays from light sources (such as windows and lamps) as they reflect, refract, and cast shadows across surfaces inside the rooms.
This allows rooms and furniture to be viewed dynamically from any camera angle or viewpoint with realistic lighting and reflections.
Consequently, potential buyers experience a much more lifelike, immersive virtual walk-through of the property.

Mentor tip

Explain how ray tracing computes light paths/reflections/shadows across viewpoints to create a realistic virtual walk-through.

(d)

4 marks

1. Homeowner privacy and physical security (2 marks): Detailed 3D walk-throughs may inadvertently capture personal family items, valuables, or the exact locations of window locks and alarm sensors, which malicious actors (burglars) could exploit to plan a break-in.
2. Misrepresentation / deceptive marketing (2 marks): Wide-angle virtual lenses, artificial lighting, or digital staging in animations may exaggerate room sizes or conceal structural defects (such as dampness or cracks), misleading prospective buyers.

Mentor tip

Provide two distinct ethical concerns (e.g., homeowner privacy/burglary security risks and buyer deception/exaggerated room quality) for 2 marks each.

Question 6

19 marks

Supermarket quarterly sales spreadsheet model, target forecasting formulas, and parallel arrays

Modelling and simulation

(a)(i)

1 mark

`=SUM(B3:E3)` (or `=B3+C3+D3+E3`).

Mentor tip

Always begin spreadsheet formulas with an equals sign `=`.

(a)(ii)

1 mark

`=AVERAGE(B3:E3)` (or `=F3/4`).

Mentor tip

Either `=AVERAGE(B3:E3)` or dividing the whole-year total by 4 (`=F3/4`) is valid.

(a)(iii)

1 mark

`=MAX(B3:E3)`

Mentor tip

Use `MAX` over the four quarterly columns `B3:E3`.

(a)(iv)

1 mark

`=MIN(B3:E3)`

Mentor tip

Use `MIN` over the four quarterly columns `B3:E3`.

(b)

5 marks

1. Store the adjustable target percentage increase `7` (or `7%`) in cell `C12` (next to the `Target increase (%)` label in row 12).
2. In cell `B16` (Bakery Apr–Jun target), enter a formula referencing `B3` and using an absolute reference to ` $C$ 12`: `=B3 * (1 + $C$ 12 / 100)` (or `=B3 * (1 + $C$ 12)` if formatted as `7%`).
3. Copy the formula across cells `C16`, `D16`, and `E16` for the remaining three quarters (`=C3*(1+ $C$ 12/100)`, `=D3*(1+ $C$ 12/100)`, `=E3*(1+ $C$ 12/100)`).
4. In cell `F16` (Whole year target), calculate `=SUM(B16:E16)` (or `=F3*(1+ $C$ 12/100)`).
5. In cell `G16` (Quarter average target), calculate `=AVERAGE(B16:E16)` (or `=F16/4`).

Target = Actual \times (1 + \frac{TargetIncrease}{100})

Mentor tip

Use an absolute cell reference (` $C$ 12`) for the 7% target cell so that copying the formula across columns B16 to G16 keeps pointing to the target percentage.

(c)

2 marks

Mentor tip

Point out that relying on a single year of unit sales (or applying one flat percentage across all departments without cost/trend data) cannot accurately predict future profit.

(d)(i)

1 mark

`=B24+B28` (or `=SUM(B24, B28)` / `=B24+B26+B27`, summing Total Wholesale costs and Total Other costs).

Mentor tip

Row 30 (`Total costs`) is the sum of row 24 (`Total` wholesale costs) and row 28 (`Total` other costs).

(d)(ii)

1 mark

`=B13-B30` (Total Revenues in `B13` minus Total costs in `B30`).

Profit = Total Revenue - Total Costs

Mentor tip

Profit in `B32` equals Total Revenue (`B13`) minus Total Costs (`B30`).

(e)

6 marks

Use a loop from `0` to `7` (for the 8 departments in `DEPARTMENT[]`), prompt the user to input each of the four quarterly sales figures into parallel arrays (`APR_JUN[]`, `JUL_SEP[]`, `OCT_DEC[]`, `JAN_MAR[]`), and compute `WHOLE_YEAR[I]` as the sum of the four quarters:
```text loop I from 0 to 7 output "Enter quarterly figures for department: ", DEPARTMENT[I] output "Apr-Jun sales: " input APR_JUN[I] output "Jul-Sept sales: " input JUL_SEP[I] output "Oct-Dec sales: " input OCT_DEC[I] output "Jan-Mar sales: " input JAN_MAR[I] WHOLE_YEAR[I] = APR_JUN[I] + JUL_SEP[I] + OCT_DEC[I] + JAN_MAR[I] end loop ```

Mentor tip

Ensure you use descriptive parallel array names for all four quarters and the annual total, include clear user prompts inside the loop, and sum the four elements into `WHOLE_YEAR[I]`.

Option C: Web science · Option

Questions 7–9 · 45 marks

Question 7

20 marks

Full URLs, HTML/JavaScript DOM rendering, static pages, client-side scripting, DNS, and mobile lossy compression

Web science

(a)

2 marks

The URL `https://www.educationalsite.org/assets/home.html` is a full (absolute) URL because it specifies every component needed to locate the exact resource:
1. Protocol/Scheme (`https://`), Subdomain (`www`), Domain name (`educationalsite`), and Top-Level Domain (`org`).
2. Directory path (`/assets/`) and specific file resource name (`home.html`).

Mentor tip

Break the URL down into all its explicit parts: scheme/protocol, subdomain + domain + TLD, directory path, and filename.

(b)

3 marks

1. Above the table, display a large Level 1 heading: **Mother tongue Languages**.
2. Below the heading, draw a bordered table (`border=1`) with two rows: the top cell contains `Mother Tongue`.
3. Note the syntax bugs in the script (`var subjects = [...]:` uses a colon instead of a semicolon, and `.InnerHTML` has a capital `I` instead of `.innerHTML`), OR if interpreted as intended, the second row displays the list of 7 languages separated by line breaks (`English`, `Spanish`, `French`, `Hindi`, `Mandarin`, `Japanese`, `Korean`) — or remains blank if the script fails due to the syntax/capitalization errors:
```text Mother tongue Languages +-------------------+ | Mother Tongue | +-------------------+ | English | | Spanish | | French | | Hindi | | Mandarin | | Japanese | | Korean | +-------------------+ ```

Mentor tip

(c)

2 marks

The webpage displays the exact same hardcoded list of languages every time it is loaded, independent of user input, time of day, or external database queries.
Changing the displayed languages requires a developer to manually edit and save the HTML/JavaScript source file.

Mentor tip

Explain that content is hardcoded in the client file with no connection to an external database or server-side script, so it never changes unless the source code is edited.

(d)

3 marks

Client-side scripting languages like JavaScript execute directly inside the user's browser to provide dynamic interactivity, DOM manipulation, and input validation without reloading the page from the server.
Because JavaScript is a universal web standard used across millions of websites, browsers must support it consistently so webpages render and function identically across different devices and operating systems.

Mentor tip

Link local browser execution of JavaScript to interactive user experiences and cross-browser standardization.

(e)

2 marks

A **protocol** (such as HTTP or TCP/IP) is a strict, formal set of rules governing how data packets are formatted, transmitted, and received during network communication.
A **standard** (such as HTML5 or W3C accessibility guidelines) is an agreed-upon technical specification or framework endorsed by an organization to ensure cross-platform compatibility during development.

Mentor tip

Protocol = rules for network communication/data transmission; Standard = agreed specification/framework for compatible development.

(f)

4 marks

1. When the user enters the URL, the browser first checks its local DNS cache (and OS cache) to see if the domain name has recently been mapped to an IP address.
2. If not cached locally, the client sends a DNS lookup query at the TCP/IP application layer to a configured recursive DNS resolver (ISP DNS server).
3. If the resolver does not have the record, it queries the hierarchy of Root, Top-Level Domain (TLD, e.g., `.org`), and Authoritative name servers that hold the master directory for that domain.
4. Once the matching IP address is found, it is returned to the user's browser so it can establish a direct HTTP/TCP connection to the web server (or an error message is returned if the domain does not exist).

Mentor tip

Trace the lookup chain: local browser cache -> DNS resolver -> TLD/authoritative server -> IP address returned to browser.

(g)

4 marks

1. Smaller file size for faster wireless transfer and storage savings (2 marks): Lossy compression achieves much higher compression ratios than lossless methods, enabling video files to download rapidly over mobile cellular networks and occupy far less limited flash storage on a smartphone.
2. Imperceptible quality loss on small screens and lower data costs (2 marks): On a compact smartphone screen, minor pixel or audio artifacts discarded by lossy compression are barely noticeable to the viewer, while the reduced data transfer saves mobile data allowances and battery power.

Mentor tip

Organize your explanation around two clusters (2 marks each): File Size/Speed/Storage and Visual Quality on small mobile screens/Data Cost.

Question 8

11 marks

Keyword vs phrase searching, breadth-first web crawling, PageRank features, and black hat SEO

Web science

(a)

2 marks

Search engines match core keywords directly against indexed page `<meta>` tags, titles, and inverted index terms.
Entering a conversational question phrase (`'Did George Washington have a diary?'`) includes common stop words (`Did`, `have`, `a`) and rigid phrasing that may either be ignored or trigger false-positive matches on unrelated pages, whereas targeted keywords (`George Washington diary`) yield more precise results.

Mentor tip

Explain that keywords match indexed meta tags/content directly while conversational phrases introduce stop words or literal phrasing ambiguities.

(b)

1 mark

`A`, `B`, `E` (visiting the root `A` first, followed by its immediate level-1 children `B` and `E` from left to right before descending to level 2).

Mentor tip

Breadth-first search visits nodes level by level: Root (`A`), then its direct children (`B`, `E`, `H`, `K`) before visiting grandchildren (`C`, `D`, etc.).

(c)

2 marks

Breadth-first crawling indexes all top-level and shallow-depth pages across websites before descending into deep link chains.
This prevents the crawler from getting trapped in deep or infinite hierarchy loops on a single site and ensures high-importance homepages and main directory pages are indexed first.

Mentor tip

Highlight that breadth-first search prioritizes higher-level, more important pages across the web and avoids getting stuck down a single deep path.

(d)

2 marks

1. It calculates a numerical authority score for each webpage based on both the quantity and the PageRank weight of incoming backlinks (and outgoing link counts).
2. It is a recursive/iterative algorithm that incorporates a damping factor (typically around `0.85`) to model the probability that a random web surfer continues clicking links.

Mentor tip

State two specific PageRank properties: weighting by incoming link importance, recursive calculation, or use of a damping factor.

(e)

4 marks

1. Inaccurate historical research and compromised academic validity (2 marks): Black hat tactics like keyword stuffing (`'George Washington diary'`), hidden text, or link farms artificially push low-quality, biased, or fabricated webpages to the top of search results, causing DP History students like Brooke to cite unreliable sources in their assignments.
2. Wasted study time and security risks (2 marks): Cloak-and-redirect or bait-and-switch pages waste students' time and bandwidth visiting irrelevant commercial sites, and may expose their computers to malware or phishing.

Mentor tip

Explicitly connect the effects of black hat SEO (inaccurate sources, wasted time, malware redirects) to DP History students like Brooke to earn full marks.

Question 9

14 marks

ARPANET distributed architecture, client-server advantages, P2P vs cloud computing, and open standards

Web science

(a)

2 marks

Fault tolerance and resilience: By distributing nodes across multiple locations without a single central switch, the military network could continue routing messages along alternative paths even if several nodes or links failed or were destroyed.
It also allowed geographically dispersed research institutions to share scarce mainframe computing resources.

Mentor tip

Identify fault tolerance/redundancy (surviving node failures) or resource sharing across geographically dispersed mainframes, and expand on how it works.

(b)

2 marks

Mentor tip

Mention either centralized security/resource management or lightweight hardware requirements for client terminals.

(c)

4 marks

1. Cloud computing (2 marks): Resources (storage, processing, software) are hosted and managed centrally in large provider data centres and delivered over the internet as scalable services (SaaS, PaaS, IaaS) with centralized control and rapid elasticity.
2. Peer-to-Peer (P2P) computing (2 marks): Architecture is decentralized with no central server; equal peer nodes directly share their own local files, bandwidth, and processing power with one another, with access controlled by individual participants.

Mentor tip

Contrast centralized data-centre service provision (Cloud) with decentralized direct resource sharing among equal nodes (P2P).

(d)

6 marks

1. Role of open standards (3 marks): Royalty-free, publicly documented protocols and formats (such as HTTP, HTML, TCP/IP, and XML) prevent any single government or corporation from monopolizing web communication. Anyone can build a web server, browser, or site without licensing fees, empowering independent publishing and global collaboration.
2. Role of interoperability (3 marks): Built on open standards, interoperability ensures that heterogeneous hardware devices, operating systems, and databases can exchange and process data seamlessly without proprietary middlemen or custom translation layers, allowing distributed nodes worldwide to form a cohesive, decentralized web.

Mentor tip

Address both Open Standards (3 marks: HTTP/HTML/TCP-IP removing proprietary gatekeepers) and Interoperability (3 marks: seamless cross-system data exchange).

Option D: Object-oriented programming · Option

Questions 10–13 · 45 marks

Question 10

14 marks

Car rental object fundamentals, accessors and mutators, default constructors, and subclass inheritance

Object-oriented programming

(a)

2 marks

Mentor tip

Mention that an object is an instance of a class combining data attributes (state) and methods (behaviour).

(b)

1 mark

`setPricePerDay(double pricePerDay)` (or `setNumberPlate`, `setBrandModel`, `setYear`, `setRentalClass`, `setFuelType`, `setTransmissionType`).

Mentor tip

Name any setter method starting with `set` followed by one of the attributes listed in the `Rental` UML diagram.

(c)

3 marks

Declare a `public` method with return type `String` and return the `brandModel` attribute:
```java public String getBrandModel() { return this.brandModel; } ```

Mentor tip

Include the `public` visibility modifier, `String` return type, empty parameter list `()`, and `return brandModel;` statement.

(d)

2 marks

A default constructor is a parameterless constructor that instantiates a new object in memory and initializes its instance variables to sensible default or `null`/`0`/`false` values.

Mentor tip

State both that it takes no parameters and that it instantiates the object with default attribute values.

(e)

2 marks

Mentor tip

Explain that `boolean` only supports 2 values, so `fuelType` must be changed to `String`, `char`, or `int` to accommodate 4 fuel types.

(f)

1 mark

Inheritance (`Car` is a subclass/child of superclass `Rental`, or `Car` **is-a** `Rental`).

Mentor tip

State `inheritance` (or `Car is-a Rental` / `Car extends Rental`).

(g)

3 marks

Use `extends Rental` to inherit existing attributes/methods, declare `private int numberOfDoors`, initialize it to `4` in the default constructor (calling `super()`), and provide its accessor/mutator:
```java public class Car extends Rental { private int numberOfDoors; public Car() { super(); this.numberOfDoors = 4; } public int getNumberOfDoors() { return this.numberOfDoors; } public void setNumberOfDoors(int n) { this.numberOfDoors = n; } } ```

Mentor tip

Include `extends Rental`, `private int numberOfDoors;`, `public Car() { numberOfDoors = 4; }`, and getter/setter methods for `numberOfDoors`.

Question 11

8 marks

OOP principles (inheritance, encapsulation, polymorphism, abstraction) and modularity

Object-oriented programming

(a)

1 mark

Inheritance.

Mentor tip

Declaring `Car` as a specialized version of `Rental` (`extends Rental`) uses inheritance.

(b)

3 marks

1. Code reuse and faster development (2 marks): Common attributes (like `numberPlate` and `pricePerDay`) and methods are written and tested once in the `Rental` superclass and automatically shared by `Car`, `Bus`, and `Van` without duplicating code.
2. Easier maintenance and extensibility (1 mark): Fixing a bug or updating a method in `Rental` immediately propagates to all vehicle subclasses, and new vehicle types can be added cleanly.

Mentor tip

Explain one benefit in detail (e.g., code reuse of tested parent methods) and identify a second benefit (e.g., reduced maintenance cost or extensibility).

(c)

2 marks

1. Encapsulation.
2. Polymorphism (or Abstraction).

Mentor tip

Name any two of the remaining core OOP pillars: Encapsulation, Polymorphism, or Abstraction.

(d)

2 marks

Mentor tip

Choose one clear advantage of modularity (easier isolated debugging/testing, parallel team development, or code readability) and explain why it occurs.

Question 12

15 marks

Parameter variables, array deduplication in findBrandModels(), and multi-criteria filtering

Object-oriented programming

(a)

2 marks

A parameter variable is a variable declared in a method's signature (header) that receives a value or object reference passed into the method when it is called.

Mentor tip

Mention both that it is declared in the method signature/header and that it receives data (by value or reference) from the caller.

(b)

8 marks

Create a `Car[] result = new Car[100]` array and a counter `count = 0`. Loop through non-null elements of `allCars`, check if `allCars[i].getBrandModel()` already matches any car in `result[0 .. count-1]` using `.equals()`, and if not found, insert `allCars[i]` at `result[count++]`:
```java public Car[] findBrandModels(Car[] allCars) { Car[] result = new Car[100]; int count = 0; for (int i = 0; i < allCars.length && allCars[i] != null; i++) { boolean found = false; for (int j = 0; j < count; j++) { if (result[j] != null && result[j].getBrandModel().equals(allCars[i].getBrandModel())) { found = true; } } if (!found) { result[count] = allCars[i]; count++; } } return result; } ```

Mentor tip

(c)

5 marks

1. Call `findBrandModels(allCars)` first and store the returned array of unique car models in a local array (e.g., `uniqueCars`).
2. Iterate through each non-null `Car` object in `uniqueCars` using a loop.
3. For each car, use accessor methods to check if all three conditions hold: `isFuelType() == true` (petrol), `isTransmissionType() == false` (or `true`, matching automatic transmission), and `getPricePerDay() < 35.0`.
4. If a car satisfies all three criteria, copy it into a `desiredCars` array (or print its details directly); if it fails any condition, skip it (or set its slot in `uniqueCars` to `null`).
5. Output or return the filtered list of matching unique cars to the customer.

Mentor tip

Be sure to call `findBrandModels(allCars)` as your first step so the results presented to the customer contain no duplicate `brandModel` entries.

Question 13

8 marks

Customer-Car object associations, circular dependency pitfalls, and database ethics

Object-oriented programming

(a)

1 mark

Draw a directed association / aggregation arrow pointing from `Customer` to `Car` (`Customer` **has-a** reference to `Car` objects in its rental history and current rental):
`[ Customer ] --------> [ Car ]` (or `[ Customer ] <>------> [ Car ]`)

Mentor tip

Show `Customer` pointing to `Car` (indicating that a `Customer` object holds references to `Car` objects).

(b)

2 marks

Adding `customerID` inside `Rental` while `Customer` already holds references to `Car` creates a circular (bidirectional) dependency where `Customer` depends on `Car` and `Car` depends on `Customer`.
This tight coupling duplicates relationship data, increases maintenance overhead when either class changes, and risks data inconsistency if one side is updated without the other.

Mentor tip

Highlight that mutual references (`Customer` has-a `Car` and `Car` has-a `Customer`) create a circular/redundant dependency that increases coupling and inconsistency risks.

(c)

5 marks

1. Obligation to protect customer privacy: Programmers must practice data minimization by collecting only personal details strictly necessary for car rental contracts, limiting exposure of private customer lives.
2. Obligation to ensure data security: Programmers must implement strong encryption, authentication, and access controls to safeguard stored addresses, IDs, and rental histories from unauthorized breaches or misuse.
3. Obligation to maintain data accuracy and integrity: Programmers should build input validation and verification mechanisms so customer records are not corrupted or falsely attributed.

Mentor tip

Our analysis

Where the marks are

Each part sorted by the topic it mostly tests. Databases carries the most marks on this paper.

Databases45 marks · 25%
Q1, Q2, Q3
Modelling and simulation45 marks · 25%
Q4, Q5, Q6
Web science45 marks · 25%
Q7, Q8, Q9
Object-oriented programming45 marks · 25%
Q10, Q11, Q12, Q13

Mentor insights

Traps to watch for

01
Databases: School bus payment transactions, concurrency locking, DBA roles, · Q2
Trace the full lifecycle of a financial transaction: initiate -> debit/credit -> commit on success or roll back on failure.
02
Modelling and simulation: Supermarket quarterly sales spreadsheet model, target forecasting · Q6
Always begin spreadsheet formulas with an equals sign `=`.
03
Web science: Full URLs, HTML/JavaScript DOM rendering, static pages, client-si · Q7
Break the URL down into all its explicit parts: scheme/protocol, subdomain + domain + TLD, directory path, and filename.
04
Object-oriented programming: Parameter variables, array deduplication in findBrandModels(), an · Q12
Mention both that it is declared in the method signature/header and that it receives data (by value or reference) from the caller.

Solutions and tips are GeorgeTheTutor's own; the questions are not reproduced here. Not affiliated with or endorsed by the International Baccalaureate Organization.

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