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Worked solutions

IB Computer Science SL · Paper 2

Computer Science, Standard Level

Session: November 2017
Marks: 180
Duration: 1 hour
Calculator: Not allowed
Questions: 12

Keep your copy of the paper open alongside. We don't reproduce the questions: each part below is labelled to match the November 2017 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

14 marks

Database transactions, ACID durability, relationship cardinalities, data dictionaries, and DBA roles

Databases

(a)

2 marks

Define a database transaction:
1) A logical unit of work comprising one or more database operations (reads or updates) executed independently.
2) Treated atomically so that it either completes in full and transitions the database to a new consistent state, or rolls back completely if interrupted.

Mentor tip

Mention both that it is a single logical unit of work and that it modifies or queries database state atomically.

(b)

2 marks

Explain the importance of durability (from ACID) in a database transaction:
1) Permanent persistence: Ensures that once a transaction is committed, its changes are written to non-volatile storage.
2) Crash resilience: Guarantees that committed data modifications are never lost even if the system immediately experiences a power outage, hardware crash, or software failure.

Mentor tip

Emphasize that committed changes survive permanently despite subsequent system crashes or power failures.

(c)

2 marks

Identify two types of entity relationships within relational databases:
1) One-to-one (1:1)
2) One-to-many (1:M / 1:N) or Many-to-many (M:N)

Mentor tip

Any two standard cardinalities (one-to-one, one-to-many, many-to-one, many-to-many) are valid.

(d)

4 marks

Describe the nature and contents of a database data dictionary:
1) Metadata repository: A centralized system table or file storing metadata (data about the structure of the database) rather than actual user records.
2) Schema definitions: Defines field names, data types, field lengths, default values, and primary/foreign key constraints for every relation.
3) Security and storage metrics: Tracks user roles, access privileges, audit logs, and physical storage space allocation.
4) Restricted system access: The DBMS consults the data dictionary before executing any query, and it is hidden from ordinary end-users to prevent accidental schema corruption.

Mentor tip

Define the data dictionary as a metadata directory and list at least three structural items it tracks (such as data types, constraints, and access rights).

(e)

4 marks

Identify four core responsibilities of a Database Administrator (DBA):
1) Designing the database schema and creating tables, indexes, and views.
2) Configuring user authentication, role-based access control, and security policies to protect sensitive data.
3) Executing routine backups and managing disaster recovery procedures.
4) Installing DBMS software patches, tuning query performance, and training staff.

Mentor tip

Provide four distinct administrative duties covering schema design, security, backups, and software maintenance.

Question 2

18 marks

Art student examination relation: data vs information, validation vs verification, and SQL queries

Databases

(a)

3 marks

Distinguish between data and information with direct reference to `CLASS_TABLE`:
1) Data definition: Raw, unorganized facts or symbols without surrounding context.
2) Information definition: Processed data that has been assigned meaning and context for human interpretation.
3) Table example: The raw integer `99` or string `"Joe Skrin"` is data, whereas knowing that `99` is Ines Prest's total year score (which means she failed because `99 < 150`) is information.

Mentor tip

Define both terms and cite a specific value from `CLASS_TABLE` (such as `99` or `"Joe Skrin"`) to illustrate the difference.

(b)(i)

1 mark

Define an entity:
A distinct real-world object, person, or concept about which data attributes are recorded and classified in a database.

Mentor tip

Describe an entity as a real-world object or person represented by attributes in a relation.

(b)(ii)

1 mark

State the specific entity represented by a row in `CLASS_TABLE`:
An art student.

Mentor tip

Each tuple in `CLASS_TABLE` stores examination marks for a single student.

(c)

1 mark

Identify an appropriate data type for `Student_ID` (e.g., `A1209`):
`String` (or `VARCHAR`, `CHAR`, alphanumeric text).

Mentor tip

Because `Student_ID` mixes letters and digits (`A1209`), it must be stored as a text/string type rather than a numeric integer.

(d)

4 marks

Explain the complementary roles of data validation and data verification:
1) Data validation role: Ensures that entered data is reasonable, sensible, and conforms to predefined syntactic rules.
2) Data validation mechanism: Automated computer checks (such as range checks, type checks, or format checks) executed during data entry.
3) Data verification role: Ensures that data entered into the system accurately matches the original source document without transcription errors.
4) Data verification mechanism: Performed via double-entry typing or visual proofreading against the source sheet, working alongside validation to guarantee overall data quality.

Mentor tip

Contrast automated rule-checking (validation: 'is it sensible?') with source-matching (verification: 'was it copied accurately?').

(e)

2 marks

Explain how the `Total` attribute in `CLASS_TABLE` can be validated:
1) Type and range check: Check that `Total` is an integer within the valid range `0` to `300` inclusive (`0 <= Total <= 300`).
2) Consistency / cross-field check: Verify that `Total` equals the exact arithmetic sum `Exam_One + Exam_Two + Exam_Three`.

0 \leq Total \leq 300 and Total = Exam_One + Exam_Two + Exam_Three

Mentor tip

Mention both the integer range check (0 to 300) and the cross-field sum check against the three exam columns.

(f)(i)

2 marks

Describe the query steps to output the names of students who scored the maximum mark (`100`) on `Exam_Two`:
1) Select the `Student_Name` field from `CLASS_TABLE`.
2) Filter records where `Exam_Two = 100`.
```sql
SELECT Student_Name FROM CLASS_TABLE WHERE Exam_Two = 100;
```

Mentor tip

Ensure you project `Student_Name` and test `Exam_Two = 100`.

(f)(ii)

4 marks

Describe the query steps to output the `Student_ID` of all students who passed (requires scoring at least 30 on every exam AND at least 150 in total):
1) Project the `Student_ID` attribute from `CLASS_TABLE`.
2) Filter rows where `Exam_One >= 30`, `Exam_Two >= 30`, and `Exam_Three >= 30`.
3) Combine with the total condition `Total >= 150` using logical `AND` operators (or negate the failing conditions using `NOT` and `OR`).
```sql
SELECT Student_ID FROM CLASS_TABLE
WHERE Exam_One >= 30 AND Exam_Two >= 30 AND Exam_Three >= 30 AND Total >= 150;
```

Mentor tip

To pass, a student must satisfy ALL FOUR conditions simultaneously (`>= 30` on each of the three exams AND `Total >= 150`), so link them with `AND`.

Question 3

13 marks

School volunteers relation: data redundancy, 1NF properties, compound keys, and 3NF normalization

Databases

(a)(i)

1 mark

State what is meant by redundant data in a database:
Unnecessary duplication where the exact same piece of data is stored in multiple places within a table or across tables.

Mentor tip

Focus on unnecessary repetition of non-key data values across multiple records.

(a)(ii)

2 marks

Explain one problem caused by redundant data:
1) Update anomalies and data inconsistency: If a school changes its address, updating it in one row while forgetting another row leaves the database with contradictory addresses, yielding unreliable query results.
2) Alternative: Wastes physical storage space by repeating identical strings (`School_Name`, `Address`) across many rows.

Mentor tip

State the issue (such as update anomalies/inconsistency or wasted storage) and explain why it occurs.

(b)

3 marks

Identify three characteristics of First Normal Form (1NF) evident in `SCHOOL_VOLUNTEERS_TABLE`:
1) Atomic values: Every cell (attribute value) in every tuple contains a single, indivisible atomic value with no repeating groups.
2) Homogeneous column domains: All values within a given column share the same data type (e.g., `Num_Volunteers` contains only integers).
3) Unique primary key and distinct tuples: Every column has a unique attribute name, no two rows are identical, and each row is uniquely identified by the composite key `(Code, Date)`.

Mentor tip

List three standard 1NF rules: atomic values, no repeating groups/duplicate rows, and uniform data types per column.

(c)

2 marks

Explain why a compound (composite) key `(Code, Date)` is required for `SCHOOL_VOLUNTEERS_TABLE`:
1) Single-attribute non-uniqueness: Neither `Code` (since the same school volunteers on multiple dates, e.g., `EE1324`) nor `Date` (since multiple schools volunteer on `10/07/2017`) can uniquely identify a tuple on its own.
2) Combined uniqueness: Combining `Code` and `Date` forms a minimal composite key that uniquely identifies each school's volunteering record on a specific date without adding a surrogate autonumber column.

Mentor tip

Show using the table data that both `Code` and `Date` repeat individually, so both are needed together to guarantee uniqueness.

(d)

5 marks

Discuss whether `SCHOOLS_TABLE(Code, School_Name, Address)` and `VOLUNTEERS_TABLE(Code, Date, Num_Volunteers)` are in Third Normal Form (3NF):
1) 3NF criteria: A relation is in 3NF if it is in 2NF (no partial dependencies on a composite key) and contains no transitive dependencies (no non-key attribute depends on another non-key attribute).
2) Evaluating `VOLUNTEERS_TABLE`: The primary key is `(Code, Date)`, and the sole non-key attribute `Num_Volunteers` depends on both the school `Code` and the `Date` together; there are no transitive dependencies, so `VOLUNTEERS_TABLE` is in 3NF.
3) Evaluating `SCHOOLS_TABLE` (Case 1 — 3NF holds): If `School_Name` is not guaranteed unique (two schools in different districts could share a name) or if both `School_Name` and `Address` depend directly and solely on the primary key `Code`, then no transitive dependency exists and `SCHOOLS_TABLE` is in 3NF.
4) Evaluating `SCHOOLS_TABLE` (Case 2 — Potential violation): However, if `School_Name` is a unique alternate key that functionally determines `Address` (`Code -> School_Name -> Address`), or if a single school name has multiple campus addresses, a transitive dependency exists.
5) Resolution if violated: In that case, `SCHOOLS_TABLE` would need further decomposition into `(Code, School_Name)` and `(School_Name, Address)` to strictly satisfy 3NF.

Mentor tip

Define 3NF (in 2NF + no transitive dependencies), confirm `VOLUNTEERS_TABLE` is in 3NF, and discuss whether `Address` transitively depends on `School_Name` in `SCHOOLS_TABLE`.

Option B: Modelling and simulation · Option

Questions 4–6 · 45 marks

Question 4

12 marks

Computer models vs simulations, modelling complexity, and ethical/practical justifications

Modelling and simulation

(a)

4 marks

Distinguish between a computer model and a computer simulation:
1) Computer model definition: A static mathematical or logical representation of a real-world system.
2) Model components: Consists of variables, data structures, and mathematical formulas/rules that define how the system behaves.
3) Computer simulation definition: A dynamic process that executes or runs the computer model over time.
4) Simulation purpose: Feeds varying input parameters into the model to observe, measure, and analyse the resulting outcomes under different conditions.

Mentor tip

Contrast the static mathematical rules/formulas (the model) with the dynamic execution of those rules using test inputs (the simulation).

(b)

2 marks

Identify two reasons why certain real-world systems are difficult to model accurately:
1) Incomplete variable identification: Not all underlying physical or human variables influencing the system are known or measurable.
2) Mathematical intractability: The interactions between variables are too complex, chaotic, or non-linear to express as exact mathematical equations.

Mentor tip

Mention unknown/unmeasurable variables and the difficulty of formulating exact mathematical relationships between them.

(c)(i)

3 marks

Describe an example where physical experimentation is intolerable for ethical reasons:
1) Concrete scenario: Testing the toxicity of experimental pharmaceuticals, starvation diets, or high-speed vehicle crash impacts on living human or animal subjects.
2) Ethical violation: Deliberately exposing living subjects to severe bodily harm, suffering, or death violates fundamental bioethical and moral standards.
3) Simulation alternative: Using a computer physiological or crash-test simulation models the biological or physical impact without harming living beings.

Mentor tip

State a specific experiment (such as animal/human drug toxicity or crash testing) and explicitly articulate the ethical harm avoided.

(c)(ii)

3 marks

State three non-ethical advantages of running a computer simulation rather than building a physical prototype:
1) Cost savings: Eliminates the expense of purchasing physical materials and constructing multiple physical prototypes.
2) Speed and time compression: Parameters can be modified instantly to observe multi-year outcomes in seconds.
3) Safe repeatability and 'what-if' testing: Destructive or extreme scenarios (such as bridge collapse or nuclear core overheating) can be repeated endlessly without physical danger.

Mentor tip

Focus on practical benefits: lower financial cost, faster iteration/time compression, and safe testing of destructive 'what-if' scenarios.

Question 5

12 marks

Manufacturing company financial spreadsheet model, validation testing, and profit strategy exploration

Modelling and simulation

(a)

6 marks

Describe a structured multi-sheet layout for the manufacturing company's financial spreadsheet model:
1) Modular worksheet separation: Organize the workbook into dedicated sheets for distinct financial domains (e.g., a `Sales_Revenue` sheet, a `Production_Costs` sheet, a `Staff_Salaries` sheet, and a master `Profit_Summary` sheet).
2) Granular itemization: Within each sheet, list individual line items in rows (such as specific manufactured products, raw material unit costs, or monthly utility bills) alongside their numeric quantities and unit prices.
3) Category-level formulas: Use built-in functions (such as `=SUM(...)`) at the bottom of each sheet to compute total revenue, total wages, and total overheads per month or product line.
4) Intermediate calculations: Incorporate formulas for derived financial obligations such as corporate tax rates (`=Gross_Profit * Tax_Rate`), depreciation, or shipping overheads.
5) Cross-sheet linking to master summary: The `Profit_Summary` sheet references category totals across sheets (`=Sales_Revenue!B50 - Production_Costs!B50 - Staff_Salaries!B50`) to compute net annual profit and multi-year projections.

Net Profit = \sum Sales Revenue - (\sum Production Costs + \sum Salaries + Tax)

Mentor tip

Name at least two specific sheet categories, mention item rows, `SUM` totals, intermediate calculations (like tax), and how the final profit formula links them.

(b)

2 marks

Suggest how to test the reliability and accuracy of the new financial spreadsheet model:
1) Historical backtesting: Input actual cost and sales figures from previous financial years into the spreadsheet model.
2) Output verification: Compare the profit and tax figures generated by the spreadsheet against the company's audited historical financial statements to verify they match.

Mentor tip

Explain how feeding known historical data from past years and comparing against actual past profits validates the model.

(c)

4 marks

Explain how the spreadsheet model can be used to investigate strategies for meeting 3-year profit targets:
1) Running 'what-if' scenarios (Goal Seek / sensitivity analysis): Management can systematically alter input variables to observe the immediate impact on projected 3-year net profit.
2) Adjusting revenue parameters: Test the effect of raising product selling prices or increasing projected sales volumes for high-margin items.
3) Adjusting cost parameters: Model the impact of switching to cheaper raw material suppliers, automating assembly lines to reduce wage growth, or discontinuing unprofitable product lines.
4) Parameter optimization: Compare the outcomes of multiple scenarios to select the most realistic combination of price adjustments and cost reductions that achieves the 3-year target.

Mentor tip

Mention 'what-if' scenario testing and give at least two specific financial variables (e.g., product selling price, sales volume, or salary/material costs) that can be tweaked.

Question 6

21 marks

Weather forecasting simulations: supercomputing advances, chaos/long-range error, historical data, and CGI visualization

Modelling and simulation

(a)

4 marks

Suggest two reasons why modern weather forecasting simulations have improved in both accuracy and range:
1) Supercomputing processing power: Modern high-performance clusters can execute vastly more complex atmospheric equations at finer spatial grid resolutions within an operational timeframe.
2) Denser sensor telemetry and scientific understanding: Global networks of weather satellites, Doppler radar, ocean buoys, and ground stations feed real-time high-density initial data into refined meteorological models.

Mentor tip

Provide two distinct factors (e.g., faster supercomputers allowing finer grid resolution, and richer satellite/sensor input data) and explain each.

(b)

4 marks

Suggest why weather forecasts lose accuracy as the prediction window extends further into the future:
1) Incomplete initial measurements: Weather stations and satellites can only sample discrete points, leaving minor localized atmospheric variables unmeasured.
2) Mathematical approximations: Complex physical processes (such as micro-turbulence and cloud formation) must be approximated in the model's differential equations.
3) Short-term negligibility: Over a 24-to-48-hour window, these tiny rounding and measurement errors have a negligible effect on the output.
4) Cumulative chaos (Butterfly Effect): In a chaotic non-linear system like the atmosphere, small initial discrepancies compound exponentially over time steps, causing long-range trajectories to diverge wildly from reality.

Mentor tip

Explain how unavoidable approximations and unmeasured minor variables compound exponentially over time (the butterfly effect).

(c)

5 marks

Discuss the extent to which historical weather data can accurately forecast future weather:
1) Model calibration and backtesting: Historical weather archives allow meteorologists to test whether their simulation equations accurately reproduce past weather transitions and tune model weights accordingly.
2) Cyclical phenomenon recognition: Studying past macro-events (such as El Niño / La Niña oscillations or seasonal monsoon cycles) helps forecasters predict how similar atmospheric setups will evolve when they recur.
3) Establishing seasonal baselines: Multi-decade records provide reliable statistical probabilities for temperature and precipitation norms in a given region.
4) Limitation — Non-stationary climate change: Historical data assumes a stable climate baseline and fails to account for unprecedented modern shifts such as accelerating greenhouse gas emissions, polar ice melt, and global warming.
5) Conclusion: While historical data is essential for calibrating physical models and understanding recurring cycles, it cannot be relied upon in isolation without incorporating real-time sensor telemetry and modern climate forcing variables.

Mentor tip

Balance the strengths of historical data (calibrating models, recognizing El Niño cycles) against its core limitation (inability to account for modern anthropogenic climate change).

(d)(i)

2 marks

Define visualization:
1) The conversion and graphical representation of abstract, complex numerical simulation data into visual formats (such as 2D/3D maps, charts, or animations).
2) Designed so that human observers can intuitively interpret patterns, trends, and spatial relationships.

Mentor tip

Include both converting abstract/numerical data into graphical form and making it easily understandable to humans.

(d)(ii)

6 marks

Discuss, with examples, how advances in visualization have made weather simulation outputs accessible to the general public:
1) Inaccessibility of raw simulation output: Weather supercomputers output massive arrays of raw floating-point numbers (isobaric pressures, wind vectors, humidity percentages) that are incomprehensible to non-experts.
2) Intuitive iconography: Modern broadcasts map numerical ranges onto universally understood visual symbols (such as sun icons, raindrop graphics, or colour-coded temperature heatmaps) overlaid on geographic maps.
3) CGI and time-lapse animation: Computer-generated imagery animates the movement of rain bands, storm fronts, and wind currents sweeping across a region over time.
4) Interactive 3D and mobile mapping: Public users can zoom into street-level interactive radar maps on smartphones to see exactly when precipitation will reach their location.
5) Public comprehension and safety: By translating abstract atmospheric grids into intuitive moving visuals, citizens can quickly grasp severe weather risks and take timely precautions.

Mentor tip

Contrast raw numerical arrays with visual symbols (raindrops/sun icons) and CGI animations (moving rain belts), explaining how this helps the general public.

Option C: Web science · Option

Questions 7–9 · 45 marks

Question 7

15 marks

Website templates: HTML characteristics, external CSS trade-offs, TCP/IP reliability, and lossy vs lossless compression

Web science

(a)

2 marks

Identify two characteristics of HyperText Markup Language (HTML):
1) Uses markup tags (such as `<h1>`, `<p>`, `<div>`) to define the semantic structure and layout of a web document.
2) Supports hypertext navigation via anchor links (`<a>`), multimedia embedding (`<img>`, `<audio>`), and integration with CSS and client-side scripts.

Mentor tip

Mention tag-based document structuring and support for hyperlinks or embedded media/scripts.

(b)

6 marks

Discuss the benefits and disadvantages of separating styling into an external CSS file alongside the HTML template:
1) Benefit — Separation of content and presentation: Designers can modify fonts, colours, and layouts inside the single CSS file without touching the structural HTML markup.
2) Benefit — Site-wide visual consistency and maintainability: Linking multiple HTML pages to one stylesheet enforces a uniform look and feel across the entire website and saves development time.
3) Benefit — Smaller HTML file size and browser caching: Eliminating inline style repetition shrinks HTML payloads, and browsers cache the CSS file after the first page load, speeding up subsequent page navigation.
4) Disadvantage — Cross-browser rendering inconsistencies: Different web browsers (or older versions) may interpret certain CSS rules or fonts slightly differently, requiring extra compatibility testing.
5) Disadvantage — Single point of styling failure / offline dependency: If the external CSS file fails to load, is accidentally deleted, or is viewed offline without the linked stylesheet, the entire website renders as unstyled plain text.
6) Disadvantage — Additional HTTP request and learning curve: Fetching a separate CSS file adds an initial HTTP request, and novice template users must understand both HTML and CSS syntax (and cascade specificity) to customize their site.

Mentor tip

Provide a balanced discussion with at least three developed benefits (maintainability, consistency, caching/file size) and two developed drawbacks (browser rendering differences, broken styling if external file fails).

(c)

3 marks

Explain how the TCP/IP protocol suite guarantees reliable downloading of the compressed template archive:
1) Packet segmentation and sequencing (TCP): TCP breaks the compressed archive into numbered packets and attaches headers containing sequence numbers and error-checking checksums.
2) Acknowledgements and retransmission (TCP): The receiving browser verifies each packet's checksum and sends an `ACK` signal back to the server; if a packet is corrupted or an `ACK` times out, TCP automatically retransmits the missing packet and reassembles them in exact sequence order.
3) Addressing and routing (IP): IP attaches destination and source IP addresses to route each packet across network hops to the correct client machine.

Mentor tip

Cover packet numbering/checksums, ACK acknowledgements with automatic retransmission of lost packets (TCP), and correct destination routing (IP).

(d)

4 marks

Evaluate lossy versus lossless compression when downloading the website template package (HTML, CSS, images, and sound effects):
1) Lossy compression mechanism and suitability: Permanently discards perceptually redundant data to achieve high compression ratios (much smaller file sizes and faster downloads); well suited for the template's web images (JPEG) and sound effects (MP3) where minor quality degradation is imperceptible.
2) Lossy limitation: Cannot be applied to text or code files because discarding bytes corrupts syntax.
3) Lossless compression mechanism and suitability: Compresses data using statistical redundancy (such as ZIP/GZIP) so the exact original bit-for-bit file is reconstructed upon decompression.
4) Synthesis for the template archive: Lossless compression is mandatory for packaging the HTML and CSS files (and the overall `.zip` archive) because even a single lost character would break the markup or stylesheet rules.

Mentor tip

Match lossy compression to the images/audio folders (smaller size, tolerable quality trade-off) and lossless compression to the HTML/CSS code files (exact bit-for-bit recovery required).

Question 8

16 marks

Open-source portal: server-side registration, third-party OAuth privacy, URL generation, and PHP string manipulation

Web science

(a)

4 marks

Evaluate the use of server-side scripting to handle user registration:
1) Advantage — Browser independence: Because the script executes on the web server and returns standard HTML, registration works reliably across all client browsers without requiring user plugins.
2) Advantage — Database integration and hidden logic: Server-side scripts connect directly to the backend user database on the server, keeping validation logic and database credentials hidden from client inspection.
3) Disadvantage — Network latency and server load: Every registration submission requires a network round-trip to the server, and high simultaneous registration traffic can bottleneck server CPU resources.
4) Disadvantage — Centralized security target: A vulnerability in the server-side script or server database could expose the central repository of registered user accounts.

Mentor tip

Weigh server-side advantages (browser independence, direct database access, hidden source code) against drawbacks (round-trip latency, server load).

(b)

4 marks

Explain how authenticating via an established third-party provider (e.g., OAuth / federated login) preserves user privacy:
1) Credential isolation: The user's sensitive password is never typed into or stored by `OpenSourceDev.org`; credentials are submitted directly to the trusted third-party identity provider over an encrypted connection.
2) Token-based verification: The third-party provider verifies the user's identity and returns only a cryptographic confirmation token (a yes/no verification and basic identifier) to the open-source portal.
3) Reduced exposure to breaches: Even if `OpenSourceDev.org` suffers a database breach, attackers cannot harvest user passwords or private social network profiles.
4) Minimal data footprint: The open-source website only stores the user's email address (for notifications) rather than accumulating sensitive personal authentication secrets.

Mentor tip

Explain that the third party verifies the password and returns a confirmation token, so `OpenSourceDev.org` never sees or stores the user's password.

(c)(i)

2 marks

Outline, with an example, how URLs for newly uploaded code resources are constructed:
1) Hierarchical path concatenation: Append the directory path and specific filename/identifier of the new code resource onto the base domain URL (`www.OpenSourceDev.org`).
2) Concrete example: `https://www.OpenSourceDev.org/releases/python/sort_module.py` (or `www.OpenSourceDev.org/newcode/script01.js`).

Mentor tip

Explain that the relative folder/file path is appended to the base domain name and provide a valid example URL.

(c)(ii)

3 marks

Outline the automated steps performed by the weekly notification script:
1) Query new resources: The script queries the server directory or database log to retrieve the list of new code URLs uploaded during the past week.
2) Compose message: It formats and inserts those generated URLs into an email notification body/template.
3) Dispatch to subscribers: It queries the registered users table for subscriber email addresses and dispatches the email batch via an SMTP mail server.

Mentor tip

State the three logical steps: fetch the list of new code URLs, embed them into an email template, and send to the list of registered subscriber emails.

(d)

3 marks

Trace the server-side PHP processing when `https://www.the2nd.org/bin.php?id=70` is submitted from IP `172.16.254.1`:
1) Form submission via POST: The HTML form sends `url = "https://www.the2nd.org/bin.php?id=70"` via HTTP `POST`; the script detects `REQUEST_METHOD == "POST"` and invokes `make_short($url)`.
2) String transformation trace inside `make_short()`:
- `make_alpha_string( $u) ‘ s t r i p s t h e p r o t oco l ‘ h ttp s ‘, t h es u b s t r in g ‘ w w w ‘, an d a l l n o n - l e tt er c ha r a c t er s (‘ : ‘, ‘/‘, ‘2‘, ‘.‘, ‘ ? ‘, ‘ = ‘, ‘7‘, ‘0‘), l e a v in g ‘$ x = "thendorgbinphpid"`.
- `first4_last4( $x) ‘ co n c a t e na t es t h e f i r s t 4 l e tt er s (‘" t h e n "‘) an d l a s t 4 l e tt er s (‘" h p i d "‘), y i e l d in g ‘$ y = "thenhpid"`.
- `limits( $x) ‘ co n c a t e na t es t h e f i r s tl e tt er (‘" t "‘) an d l a s tl e tt er (‘" d "‘), y i e l d in g ‘$ z = "td"`.
- Concatenating ` $y .".".$ z` produces `$short = "thenhpid.td"`.
3) Database insertion: The script executes `mysql_query` to insert the record triple `('https://www.the2nd.org/bin.php?id=70', 'thenhpid.td', '172.16.254.1')` into the `url_db` table.

Mentor tip

Carefully trace `$x = "thendorgbinphpid"` (removing `https`, `www`, digits `2`, `7`, `0`, and punctuation) to derive the exact shortened string `"thenhpid.td"` and the inserted database tuple.

Question 9

14 marks

Museum website redesign: static vs dynamic web pages, interactive services, PageRank, and SEO meta-tags

Web science

(a)

3 marks

Identify three differences between a static web page and a dynamic web page:
1) Content customization: A static page delivers the exact same fixed HTML content to every visitor, whereas a dynamic page generates customized content on the fly based on user queries or preferences.
2) Database and script integration: Dynamic pages execute server-side/client-side scripts and query backend databases to assemble content, whereas static pages consist solely of pre-written HTML files stored on the server.
3) Interactivity and updating: Dynamic pages allow interactive user input (search filters, booking forms) without manually editing HTML files, whereas updating a static page requires an administrator to rewrite and re-upload the HTML source code.

Mentor tip

Contrast fixed HTML views for all users (static) against script/database-driven personalized views and user interactivity (dynamic).

(b)

4 marks

Suggest two dynamic web services for the museum and state the benefit of each:
1) Service 1 — Online ticket booking and donation portal: Allows visitors to reserve timed entry tickets, book school tours, or make charitable donations online. Benefit: Generates direct funding revenue and improves visitor convenience by eliminating ticket queues.
2) Service 2 — Interactive searchable 3D virtual exhibition / downloadable audio guide: Enables global users to filter artefacts by historical era or preview exhibits virtually. Benefit: Dramatically increases public engagement, educational reach, and foot traffic to the physical museum.

Mentor tip

Pair each concrete dynamic feature (e.g., online ticket/donation checkout, interactive virtual tour) with a clear benefit addressing the museum's funding or visitor numbers.

(c)

4 marks

Explain how adding interactive online services improves the museum's search engine ranking:
1) Increased visitor traffic and dwell time: Interactive virtual tours and ticket portals attract more visitors and keep users engaged on the site longer.
2) Growth of authoritative inbound links (backlinks): External organizations (such as tourist boards, schools, universities, and local government portals) will link to the museum's interactive resources and booking pages.
3) PageRank / authority boost: Search engine ranking algorithms (like PageRank) weight incoming links from reputable external domains heavily as votes of authority.
4) Fresh indexed content: Frequent updates to events and dynamic exhibitions signal to web crawlers that the site is active and relevant, elevating its position in search results.

Mentor tip

Connect interactive services -> external links from tourist boards/schools (backlinks) + higher traffic -> higher PageRank score.

(d)

3 marks

Suggest how cataloguing museum artefacts with HTML `<meta>` tags improves Search Engine Optimization (SEO):
1) Explicit keyword and description metadata: `<meta name="keywords">` and `<meta name="description">` tags summarize each artefact's historical period, artist, and medium in the HTML `<head>`.
2) Accurate crawler indexing: When search engine spiders crawl the catalogue, they parse these meta-tags (alongside robot directives like `index, follow` and language tags) to classify and index each piece accurately in the search database.
3) Higher relevance matching and click-through: When users search for specific historical artefacts, the search engine matches their query against the indexed meta-keywords and displays the meta-description snippet, improving both ranking relevance and visitor click-through rates.

Mentor tip

Explain the three-step chain: meta-tags describe artefact keywords -> web crawlers read them to index the page -> search engines rank the page higher for matching user queries.

Option D: Object-oriented programming · Option

Questions 10–12 · 45 marks

Question 10

14 marks

Restaurant Payment and FoodItem classes: attribute initialization, static members, data types, and mutators

Object-oriented programming

(a)

2 marks

Outline how `fiCount` and `diCount` can be initialized to `0` without writing assignment statements inside the constructor:
1) Direct declaration initialization: Assign the initial value directly when declaring the instance variables at the top of the `Payment` class (`private int fiCount = 0;` and `private int diCount = 0;`).
2) Default Java primitive behaviour: Alternatively, in Java, numeric `int` instance variables are automatically initialized to `0` by default when an object is instantiated.

Mentor tip

Write `private int fiCount = 0;` in the class attribute declaration section outside the constructor.

(b)

2 marks

State the implication of the `static` keyword on variables (`foodTax`, `drinkTax`) and methods (`findPrice`) in the `Payment` class:
1) Class-level ownership: `static` attributes belong to the `Payment` class itself rather than to any individual `Payment` object, so a single shared copy exists in memory across all 50 restaurant tables.
2) Object-independent invocation: `static` methods (like `Payment.findPrice(...)` or `Payment.getFoodTax()`) can be invoked directly using the class name without instantiating a `Payment` object.

Mentor tip

Do not confuse `static` with `final` (`static` variables CAN be changed, but their value is shared across all instances of the class).

(c)

4 marks

Explain the benefits of choosing specific data types using two examples from `Payment` and `FoodItem`:
1) Example 1 — `double` for `foodTax` / prices vs `int` for `quantity` / `fiCount`: Declaring `foodTax` as `double` allows fractional decimal values (`0.2`) required for accurate financial tax calculations, whereas declaring `quantity` as `int` restricts item counts to whole numbers and uses less memory (32 bits vs 64 bits).
2) Example 2 — `String` for `itemCode` vs `FoodItem[]` array for `fi`: Declaring `itemCode` as `String` allows alphanumeric codes like `"f102"` that do not require arithmetic, while declaring `fi` as a `FoodItem[]` object array groups up to 100 ordered items under a single indexed identifier for easy loop processing.

Mentor tip

Give two concrete attribute examples from the code and explain the specific benefit (such as decimal precision, memory efficiency, or valid operations) of each type.

(d)

3 marks

Describe the purpose of the statement `private FoodItem[] fi = new FoodItem[100];`:
1) Array declaration and type: Declares an array reference variable named `fi` that holds elements of object type `FoodItem`.
2) Memory instantiation: Allocates memory space for a fixed maximum capacity of `100` `FoodItem` references.
3) Encapsulation: The `private` modifier restricts direct access so only methods inside the `Payment` class can read or modify the `fi` array.

Mentor tip

Cover all three parts of the statement: `private` (encapsulation), `FoodItem[] fi` (array of FoodItem objects), and `new FoodItem[100]` (capacity of 100).

(e)

3 marks

Construct the `addFoodItem(FoodItem f)` method in the `Payment` class to append a `FoodItem` and increment the counter:
```java
public void addFoodItem(FoodItem f) {
fi[fiCount] = f;
fiCount = fiCount + 1; // or fiCount++;
}
```

Mentor tip

Include the correct `public void` method header with a `FoodItem` parameter, store the parameter at index `fiCount`, and increment `fiCount`.

Question 11

18 marks

Tracing Payment driver code, accessor chaining, linear search findPrice(), and calculateBill()

Object-oriented programming

(a)

3 marks

Trace the three `System.out.println` statements in the driver code:
1) `tables[1].getFiCount()` -> Two `FoodItem` objects (`a` and `b`) were added to `tables[1]`: outputs `2`
2) `Payment.getFoodTax()` -> Returns the static `foodTax` value: outputs `0.2`
3) `tables[2].getDi(1).getItemCode()` -> Index `0` of `tables[2]`'s `di` array holds `c` (`"d102"`), and index `1` holds the second added `DrinkItem` (`"d103"`): outputs `d103`

Mentor tip

Remember Java arrays are 0-indexed, so `getDi(1)` retrieves the SECOND drink item added to `tables[2]` (`"d103"`).

(b)(i)

1 mark

Write a statement to print the number of drink items ordered by table 40:
```java
System.out.println(tables[40].getDiCount());
```

Mentor tip

Access `tables[40]` and invoke the `getDiCount()` accessor.

(b)(ii)

1 mark

Write a statement to print the item code of the third food item (index 2) ordered by table 2:
```java
System.out.println(tables[2].getFi(2).getItemCode());
```

Mentor tip

The third food item is at 0-based index `2`, so chain `getFi(2).getItemCode()` on `tables[2]`.

(c)

6 marks

Construct `findPrice(Item[] pl, String c)` in `Payment` using a loop with early exit to return the unit price of item code `c`:
```java
public static double findPrice(Item[] pl, String c) {
int i = 0;
double price = 0.0;
boolean found = false;
while (i < pl.length && !found) {
if (pl[i] != null && pl[i].getCode().equals(c)) {
price = pl[i].getPrice();
found = true;
}
i++;
}
return price;
}
```

Mentor tip

Use a `while` loop with a `boolean found` flag (or `return pl[i].getPrice();` early exit) and use `.getCode()` and `.getPrice()` accessors.

(d)

7 marks

Construct the `calculateBill(Item[] pl)` method in `Payment` to compute the total tax-inclusive bill for both food and drink items:
```java
public double calculateBill(Item[] pl) {
double total = 0.0;
for (int i = 0; i < fiCount; i++) {
String code = fi[i].getItemCode();
double unitPrice = findPrice(pl, code);
total = total + (fi[i].getQuantity() * unitPrice * (1.0 + foodTax));
}
for (int j = 0; j < diCount; j++) {
String code = di[j].getItemCode();
double unitPrice = findPrice(pl, code);
total = total + (di[j].getQuantity() * unitPrice * (1.0 + drinkTax));
}
return total;
}
```

Total = i = 0 \sum fiCount - 1 q_{i} p_{i} (1 + foodTax) + j = 0 \sum diCount - 1 q_{j} p_{j} (1 + drinkTax)

Mentor tip

Loop through `fi` up to `fiCount` (multiplying by `1 + foodTax`) and `di` up to `diCount` (multiplying by `1 + drinkTax`), calling `findPrice(pl, code)` for each item.

Question 12

13 marks

UML class relationships, team benefits of encapsulation, and inheritance across business units

Object-oriented programming

(a)

3 marks

Construct the UML class relationship diagram connecting `Payment`, `FoodItem`, `DrinkItem`, and `Item`:
1) Draw four class boxes labelled `Payment`, `FoodItem`, `DrinkItem`, and `Item`.
2) Draw a `'has a'` (aggregation/composition) arrow from `Payment` to `FoodItem` and another `'has a'` arrow from `Payment` to `DrinkItem` (since `Payment` contains arrays `fi` and `di`).
3) Draw a `'uses'` (dependency) arrow from `Payment` to `Item` (since `Payment.findPrice()` and `calculateBill()` take `Item[] pl` as a parameter).

Mentor tip

Clearly label the arrows from `Payment` to `FoodItem`/`DrinkItem` as 'has a' and the arrow from `Payment` to `Item` as 'uses'.

(b)

6 marks

Describe two benefits of encapsulation for the programming team, referencing the restaurant classes:
1) Benefit 1 — Data protection and prevented side-effects: Declaring attributes `private` (such as `private int quantity` in `FoodItem` or `private int fiCount` in `Payment`) prevents external classes from accidentally overwriting or corrupting internal object state.
2) Benefit 1 — Independent variable naming: Because attributes are locally scoped and hidden inside their class, different developers working on `FoodItem`, `DrinkItem`, and `Item` can freely reuse variable names like `code` or `quantity` without naming collisions.
3) Benefit 2 — Modularity and cohesive code organization: Bundling related data (`fi`, `di`, tax rates) and the methods that operate on them (`addFoodItem()`, `calculateBill()`) inside `Payment` creates a self-contained module.
4) Benefit 2 — Parallel team maintenance: One programmer can modify the internal implementation of `Payment.calculateBill()` without breaking code written by another team member in the driver class, provided the public method signatures remain unchanged.

Mentor tip

For each of the two benefits (data protection/scope isolation and modularity/maintainability), cite a specific class and attribute/method from the paper.

(c)

4 marks

Explain how inheritance improves design clarity and reduces code duplication across the company's restaurant, hotel, shop, and car hire businesses:
1) Superclass abstraction: Define a generic `Payment` (or `SaleItem`) superclass containing attributes and methods common to all business units (such as invoice date, customer ID, basic tax calculation, and total summation).
2) Subclass specialization: Create business-specific subclasses (`RestaurantPayment`, `HotelPayment`, `CarHirePayment`, or `FoodItem` / `DrinkItem` extending `MenuItem`) that inherit all shared superclass attributes and methods.
3) Code reduction: Shared billing and lookup code is written and tested only once in the superclass rather than being duplicated across four separate business programs.
4) Design clarity and overriding: The hierarchical structure clearly documents how business entities relate, while subclasses can add specialized fields (e.g., room number or rental days) and override `calculateBill()` if specific tax rules apply.

Mentor tip

Explain both how a superclass eliminates duplicated code across the businesses and how a clear hierarchy with method overriding improves design clarity.

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

Mentor insights

Traps to watch for

01
Databases: Art student examination relation: data vs information, validation · Q2
Define both terms and cite a specific value from `CLASS_TABLE` (such as `99` or `"Joe Skrin"`) to illustrate the difference.
02
Modelling and simulation: Weather forecasting simulations: supercomputing advances, chaos/l · Q6
Provide two distinct factors (e.g., faster supercomputers allowing finer grid resolution, and richer satellite/sensor input data) and explain each.
03
Web science: Open-source portal: server-side registration, third-party OAuth p · Q8
Weigh server-side advantages (browser independence, direct database access, hidden source code) against drawbacks (round-trip latency, server load).
04
Object-oriented programming: Tracing Payment driver code, accessor chaining, linear search fin · Q11
Remember Java arrays are 0-indexed, so `getDi(1)` retrieves the SECOND drink item added to `tables[2]` (`"d103"`).

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: November 2017
Marks: 180
Duration: 1 hour
Calculator: Not allowed
Questions: 12

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

Keep your copy of the paper open alongside. We don't reproduce the questions: each part below is labelled to match the November 2017 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

14 marks

Database transactions, ACID durability, relationship cardinalities, data dictionaries, and DBA roles

Databases

(a)

2 marks

Define a database transaction:
1) A logical unit of work comprising one or more database operations (reads or updates) executed independently.
2) Treated atomically so that it either completes in full and transitions the database to a new consistent state, or rolls back completely if interrupted.

Mentor tip

Mention both that it is a single logical unit of work and that it modifies or queries database state atomically.

(b)

2 marks

Explain the importance of durability (from ACID) in a database transaction:
1) Permanent persistence: Ensures that once a transaction is committed, its changes are written to non-volatile storage.
2) Crash resilience: Guarantees that committed data modifications are never lost even if the system immediately experiences a power outage, hardware crash, or software failure.

Mentor tip

Emphasize that committed changes survive permanently despite subsequent system crashes or power failures.

(c)

2 marks

Identify two types of entity relationships within relational databases:
1) One-to-one (1:1)
2) One-to-many (1:M / 1:N) or Many-to-many (M:N)

Mentor tip

Any two standard cardinalities (one-to-one, one-to-many, many-to-one, many-to-many) are valid.

(d)

4 marks

Describe the nature and contents of a database data dictionary:
1) Metadata repository: A centralized system table or file storing metadata (data about the structure of the database) rather than actual user records.
2) Schema definitions: Defines field names, data types, field lengths, default values, and primary/foreign key constraints for every relation.
3) Security and storage metrics: Tracks user roles, access privileges, audit logs, and physical storage space allocation.
4) Restricted system access: The DBMS consults the data dictionary before executing any query, and it is hidden from ordinary end-users to prevent accidental schema corruption.

Mentor tip

Define the data dictionary as a metadata directory and list at least three structural items it tracks (such as data types, constraints, and access rights).

(e)

4 marks

Identify four core responsibilities of a Database Administrator (DBA):
1) Designing the database schema and creating tables, indexes, and views.
2) Configuring user authentication, role-based access control, and security policies to protect sensitive data.
3) Executing routine backups and managing disaster recovery procedures.
4) Installing DBMS software patches, tuning query performance, and training staff.

Mentor tip

Provide four distinct administrative duties covering schema design, security, backups, and software maintenance.

Question 2

18 marks

Art student examination relation: data vs information, validation vs verification, and SQL queries

Databases

(a)

3 marks

Distinguish between data and information with direct reference to `CLASS_TABLE`:
1) Data definition: Raw, unorganized facts or symbols without surrounding context.
2) Information definition: Processed data that has been assigned meaning and context for human interpretation.
3) Table example: The raw integer `99` or string `"Joe Skrin"` is data, whereas knowing that `99` is Ines Prest's total year score (which means she failed because `99 < 150`) is information.

Mentor tip

Define both terms and cite a specific value from `CLASS_TABLE` (such as `99` or `"Joe Skrin"`) to illustrate the difference.

(b)(i)

1 mark

Define an entity:
A distinct real-world object, person, or concept about which data attributes are recorded and classified in a database.

Mentor tip

Describe an entity as a real-world object or person represented by attributes in a relation.

(b)(ii)

1 mark

State the specific entity represented by a row in `CLASS_TABLE`:
An art student.

Mentor tip

Each tuple in `CLASS_TABLE` stores examination marks for a single student.

(c)

1 mark

Identify an appropriate data type for `Student_ID` (e.g., `A1209`):
`String` (or `VARCHAR`, `CHAR`, alphanumeric text).

Mentor tip

Because `Student_ID` mixes letters and digits (`A1209`), it must be stored as a text/string type rather than a numeric integer.

(d)

4 marks

Explain the complementary roles of data validation and data verification:
1) Data validation role: Ensures that entered data is reasonable, sensible, and conforms to predefined syntactic rules.
2) Data validation mechanism: Automated computer checks (such as range checks, type checks, or format checks) executed during data entry.
3) Data verification role: Ensures that data entered into the system accurately matches the original source document without transcription errors.
4) Data verification mechanism: Performed via double-entry typing or visual proofreading against the source sheet, working alongside validation to guarantee overall data quality.

Mentor tip

Contrast automated rule-checking (validation: 'is it sensible?') with source-matching (verification: 'was it copied accurately?').

(e)

2 marks

Explain how the `Total` attribute in `CLASS_TABLE` can be validated:
1) Type and range check: Check that `Total` is an integer within the valid range `0` to `300` inclusive (`0 <= Total <= 300`).
2) Consistency / cross-field check: Verify that `Total` equals the exact arithmetic sum `Exam_One + Exam_Two + Exam_Three`.

0 \leq Total \leq 300 and Total = Exam_One + Exam_Two + Exam_Three

Mentor tip

Mention both the integer range check (0 to 300) and the cross-field sum check against the three exam columns.

(f)(i)

2 marks

Describe the query steps to output the names of students who scored the maximum mark (`100`) on `Exam_Two`:
1) Select the `Student_Name` field from `CLASS_TABLE`.
2) Filter records where `Exam_Two = 100`.
```sql
SELECT Student_Name FROM CLASS_TABLE WHERE Exam_Two = 100;
```

Mentor tip

Ensure you project `Student_Name` and test `Exam_Two = 100`.

(f)(ii)

4 marks

Describe the query steps to output the `Student_ID` of all students who passed (requires scoring at least 30 on every exam AND at least 150 in total):
1) Project the `Student_ID` attribute from `CLASS_TABLE`.
2) Filter rows where `Exam_One >= 30`, `Exam_Two >= 30`, and `Exam_Three >= 30`.
3) Combine with the total condition `Total >= 150` using logical `AND` operators (or negate the failing conditions using `NOT` and `OR`).
```sql
SELECT Student_ID FROM CLASS_TABLE
WHERE Exam_One >= 30 AND Exam_Two >= 30 AND Exam_Three >= 30 AND Total >= 150;
```

Mentor tip

To pass, a student must satisfy ALL FOUR conditions simultaneously (`>= 30` on each of the three exams AND `Total >= 150`), so link them with `AND`.

Question 3

13 marks

School volunteers relation: data redundancy, 1NF properties, compound keys, and 3NF normalization

Databases

(a)(i)

1 mark

State what is meant by redundant data in a database:
Unnecessary duplication where the exact same piece of data is stored in multiple places within a table or across tables.

Mentor tip

Focus on unnecessary repetition of non-key data values across multiple records.

(a)(ii)

2 marks

Explain one problem caused by redundant data:
1) Update anomalies and data inconsistency: If a school changes its address, updating it in one row while forgetting another row leaves the database with contradictory addresses, yielding unreliable query results.
2) Alternative: Wastes physical storage space by repeating identical strings (`School_Name`, `Address`) across many rows.

Mentor tip

State the issue (such as update anomalies/inconsistency or wasted storage) and explain why it occurs.

(b)

3 marks

Identify three characteristics of First Normal Form (1NF) evident in `SCHOOL_VOLUNTEERS_TABLE`:
1) Atomic values: Every cell (attribute value) in every tuple contains a single, indivisible atomic value with no repeating groups.
2) Homogeneous column domains: All values within a given column share the same data type (e.g., `Num_Volunteers` contains only integers).
3) Unique primary key and distinct tuples: Every column has a unique attribute name, no two rows are identical, and each row is uniquely identified by the composite key `(Code, Date)`.

Mentor tip

List three standard 1NF rules: atomic values, no repeating groups/duplicate rows, and uniform data types per column.

(c)

2 marks

Explain why a compound (composite) key `(Code, Date)` is required for `SCHOOL_VOLUNTEERS_TABLE`:
1) Single-attribute non-uniqueness: Neither `Code` (since the same school volunteers on multiple dates, e.g., `EE1324`) nor `Date` (since multiple schools volunteer on `10/07/2017`) can uniquely identify a tuple on its own.
2) Combined uniqueness: Combining `Code` and `Date` forms a minimal composite key that uniquely identifies each school's volunteering record on a specific date without adding a surrogate autonumber column.

Mentor tip

Show using the table data that both `Code` and `Date` repeat individually, so both are needed together to guarantee uniqueness.

(d)

5 marks

Discuss whether `SCHOOLS_TABLE(Code, School_Name, Address)` and `VOLUNTEERS_TABLE(Code, Date, Num_Volunteers)` are in Third Normal Form (3NF):
1) 3NF criteria: A relation is in 3NF if it is in 2NF (no partial dependencies on a composite key) and contains no transitive dependencies (no non-key attribute depends on another non-key attribute).
2) Evaluating `VOLUNTEERS_TABLE`: The primary key is `(Code, Date)`, and the sole non-key attribute `Num_Volunteers` depends on both the school `Code` and the `Date` together; there are no transitive dependencies, so `VOLUNTEERS_TABLE` is in 3NF.
3) Evaluating `SCHOOLS_TABLE` (Case 1 — 3NF holds): If `School_Name` is not guaranteed unique (two schools in different districts could share a name) or if both `School_Name` and `Address` depend directly and solely on the primary key `Code`, then no transitive dependency exists and `SCHOOLS_TABLE` is in 3NF.
4) Evaluating `SCHOOLS_TABLE` (Case 2 — Potential violation): However, if `School_Name` is a unique alternate key that functionally determines `Address` (`Code -> School_Name -> Address`), or if a single school name has multiple campus addresses, a transitive dependency exists.
5) Resolution if violated: In that case, `SCHOOLS_TABLE` would need further decomposition into `(Code, School_Name)` and `(School_Name, Address)` to strictly satisfy 3NF.

Mentor tip

Define 3NF (in 2NF + no transitive dependencies), confirm `VOLUNTEERS_TABLE` is in 3NF, and discuss whether `Address` transitively depends on `School_Name` in `SCHOOLS_TABLE`.

Option B: Modelling and simulation · Option

Questions 4–6 · 45 marks

Question 4

12 marks

Computer models vs simulations, modelling complexity, and ethical/practical justifications

Modelling and simulation

(a)

4 marks

Distinguish between a computer model and a computer simulation:
1) Computer model definition: A static mathematical or logical representation of a real-world system.
2) Model components: Consists of variables, data structures, and mathematical formulas/rules that define how the system behaves.
3) Computer simulation definition: A dynamic process that executes or runs the computer model over time.
4) Simulation purpose: Feeds varying input parameters into the model to observe, measure, and analyse the resulting outcomes under different conditions.

Mentor tip

Contrast the static mathematical rules/formulas (the model) with the dynamic execution of those rules using test inputs (the simulation).

(b)

2 marks

Identify two reasons why certain real-world systems are difficult to model accurately:
1) Incomplete variable identification: Not all underlying physical or human variables influencing the system are known or measurable.
2) Mathematical intractability: The interactions between variables are too complex, chaotic, or non-linear to express as exact mathematical equations.

Mentor tip

Mention unknown/unmeasurable variables and the difficulty of formulating exact mathematical relationships between them.

(c)(i)

3 marks

Describe an example where physical experimentation is intolerable for ethical reasons:
1) Concrete scenario: Testing the toxicity of experimental pharmaceuticals, starvation diets, or high-speed vehicle crash impacts on living human or animal subjects.
2) Ethical violation: Deliberately exposing living subjects to severe bodily harm, suffering, or death violates fundamental bioethical and moral standards.
3) Simulation alternative: Using a computer physiological or crash-test simulation models the biological or physical impact without harming living beings.

Mentor tip

State a specific experiment (such as animal/human drug toxicity or crash testing) and explicitly articulate the ethical harm avoided.

(c)(ii)

3 marks

State three non-ethical advantages of running a computer simulation rather than building a physical prototype:
1) Cost savings: Eliminates the expense of purchasing physical materials and constructing multiple physical prototypes.
2) Speed and time compression: Parameters can be modified instantly to observe multi-year outcomes in seconds.
3) Safe repeatability and 'what-if' testing: Destructive or extreme scenarios (such as bridge collapse or nuclear core overheating) can be repeated endlessly without physical danger.

Mentor tip

Focus on practical benefits: lower financial cost, faster iteration/time compression, and safe testing of destructive 'what-if' scenarios.

Question 5

12 marks

Manufacturing company financial spreadsheet model, validation testing, and profit strategy exploration

Modelling and simulation

(a)

6 marks

Describe a structured multi-sheet layout for the manufacturing company's financial spreadsheet model:
1) Modular worksheet separation: Organize the workbook into dedicated sheets for distinct financial domains (e.g., a `Sales_Revenue` sheet, a `Production_Costs` sheet, a `Staff_Salaries` sheet, and a master `Profit_Summary` sheet).
2) Granular itemization: Within each sheet, list individual line items in rows (such as specific manufactured products, raw material unit costs, or monthly utility bills) alongside their numeric quantities and unit prices.
3) Category-level formulas: Use built-in functions (such as `=SUM(...)`) at the bottom of each sheet to compute total revenue, total wages, and total overheads per month or product line.
4) Intermediate calculations: Incorporate formulas for derived financial obligations such as corporate tax rates (`=Gross_Profit * Tax_Rate`), depreciation, or shipping overheads.
5) Cross-sheet linking to master summary: The `Profit_Summary` sheet references category totals across sheets (`=Sales_Revenue!B50 - Production_Costs!B50 - Staff_Salaries!B50`) to compute net annual profit and multi-year projections.

Net Profit = \sum Sales Revenue - (\sum Production Costs + \sum Salaries + Tax)

Mentor tip

Name at least two specific sheet categories, mention item rows, `SUM` totals, intermediate calculations (like tax), and how the final profit formula links them.

(b)

2 marks

Suggest how to test the reliability and accuracy of the new financial spreadsheet model:
1) Historical backtesting: Input actual cost and sales figures from previous financial years into the spreadsheet model.
2) Output verification: Compare the profit and tax figures generated by the spreadsheet against the company's audited historical financial statements to verify they match.

Mentor tip

Explain how feeding known historical data from past years and comparing against actual past profits validates the model.

(c)

4 marks

Explain how the spreadsheet model can be used to investigate strategies for meeting 3-year profit targets:
1) Running 'what-if' scenarios (Goal Seek / sensitivity analysis): Management can systematically alter input variables to observe the immediate impact on projected 3-year net profit.
2) Adjusting revenue parameters: Test the effect of raising product selling prices or increasing projected sales volumes for high-margin items.
3) Adjusting cost parameters: Model the impact of switching to cheaper raw material suppliers, automating assembly lines to reduce wage growth, or discontinuing unprofitable product lines.
4) Parameter optimization: Compare the outcomes of multiple scenarios to select the most realistic combination of price adjustments and cost reductions that achieves the 3-year target.

Mentor tip

Mention 'what-if' scenario testing and give at least two specific financial variables (e.g., product selling price, sales volume, or salary/material costs) that can be tweaked.

Question 6

21 marks

Weather forecasting simulations: supercomputing advances, chaos/long-range error, historical data, and CGI visualization

Modelling and simulation

(a)

4 marks

Suggest two reasons why modern weather forecasting simulations have improved in both accuracy and range:
1) Supercomputing processing power: Modern high-performance clusters can execute vastly more complex atmospheric equations at finer spatial grid resolutions within an operational timeframe.
2) Denser sensor telemetry and scientific understanding: Global networks of weather satellites, Doppler radar, ocean buoys, and ground stations feed real-time high-density initial data into refined meteorological models.

Mentor tip

Provide two distinct factors (e.g., faster supercomputers allowing finer grid resolution, and richer satellite/sensor input data) and explain each.

(b)

4 marks

Suggest why weather forecasts lose accuracy as the prediction window extends further into the future:
1) Incomplete initial measurements: Weather stations and satellites can only sample discrete points, leaving minor localized atmospheric variables unmeasured.
2) Mathematical approximations: Complex physical processes (such as micro-turbulence and cloud formation) must be approximated in the model's differential equations.
3) Short-term negligibility: Over a 24-to-48-hour window, these tiny rounding and measurement errors have a negligible effect on the output.
4) Cumulative chaos (Butterfly Effect): In a chaotic non-linear system like the atmosphere, small initial discrepancies compound exponentially over time steps, causing long-range trajectories to diverge wildly from reality.

Mentor tip

Explain how unavoidable approximations and unmeasured minor variables compound exponentially over time (the butterfly effect).

(c)

5 marks

Discuss the extent to which historical weather data can accurately forecast future weather:
1) Model calibration and backtesting: Historical weather archives allow meteorologists to test whether their simulation equations accurately reproduce past weather transitions and tune model weights accordingly.
2) Cyclical phenomenon recognition: Studying past macro-events (such as El Niño / La Niña oscillations or seasonal monsoon cycles) helps forecasters predict how similar atmospheric setups will evolve when they recur.
3) Establishing seasonal baselines: Multi-decade records provide reliable statistical probabilities for temperature and precipitation norms in a given region.
4) Limitation — Non-stationary climate change: Historical data assumes a stable climate baseline and fails to account for unprecedented modern shifts such as accelerating greenhouse gas emissions, polar ice melt, and global warming.
5) Conclusion: While historical data is essential for calibrating physical models and understanding recurring cycles, it cannot be relied upon in isolation without incorporating real-time sensor telemetry and modern climate forcing variables.

Mentor tip

Balance the strengths of historical data (calibrating models, recognizing El Niño cycles) against its core limitation (inability to account for modern anthropogenic climate change).

(d)(i)

2 marks

Define visualization:
1) The conversion and graphical representation of abstract, complex numerical simulation data into visual formats (such as 2D/3D maps, charts, or animations).
2) Designed so that human observers can intuitively interpret patterns, trends, and spatial relationships.

Mentor tip

Include both converting abstract/numerical data into graphical form and making it easily understandable to humans.

(d)(ii)

6 marks

Discuss, with examples, how advances in visualization have made weather simulation outputs accessible to the general public:
1) Inaccessibility of raw simulation output: Weather supercomputers output massive arrays of raw floating-point numbers (isobaric pressures, wind vectors, humidity percentages) that are incomprehensible to non-experts.
2) Intuitive iconography: Modern broadcasts map numerical ranges onto universally understood visual symbols (such as sun icons, raindrop graphics, or colour-coded temperature heatmaps) overlaid on geographic maps.
3) CGI and time-lapse animation: Computer-generated imagery animates the movement of rain bands, storm fronts, and wind currents sweeping across a region over time.
4) Interactive 3D and mobile mapping: Public users can zoom into street-level interactive radar maps on smartphones to see exactly when precipitation will reach their location.
5) Public comprehension and safety: By translating abstract atmospheric grids into intuitive moving visuals, citizens can quickly grasp severe weather risks and take timely precautions.

Mentor tip

Contrast raw numerical arrays with visual symbols (raindrops/sun icons) and CGI animations (moving rain belts), explaining how this helps the general public.

Option C: Web science · Option

Questions 7–9 · 45 marks

Question 7

15 marks

Website templates: HTML characteristics, external CSS trade-offs, TCP/IP reliability, and lossy vs lossless compression

Web science

(a)

2 marks

Identify two characteristics of HyperText Markup Language (HTML):
1) Uses markup tags (such as `<h1>`, `<p>`, `<div>`) to define the semantic structure and layout of a web document.
2) Supports hypertext navigation via anchor links (`<a>`), multimedia embedding (`<img>`, `<audio>`), and integration with CSS and client-side scripts.

Mentor tip

Mention tag-based document structuring and support for hyperlinks or embedded media/scripts.

(b)

6 marks

Discuss the benefits and disadvantages of separating styling into an external CSS file alongside the HTML template:
1) Benefit — Separation of content and presentation: Designers can modify fonts, colours, and layouts inside the single CSS file without touching the structural HTML markup.
2) Benefit — Site-wide visual consistency and maintainability: Linking multiple HTML pages to one stylesheet enforces a uniform look and feel across the entire website and saves development time.
3) Benefit — Smaller HTML file size and browser caching: Eliminating inline style repetition shrinks HTML payloads, and browsers cache the CSS file after the first page load, speeding up subsequent page navigation.
4) Disadvantage — Cross-browser rendering inconsistencies: Different web browsers (or older versions) may interpret certain CSS rules or fonts slightly differently, requiring extra compatibility testing.
5) Disadvantage — Single point of styling failure / offline dependency: If the external CSS file fails to load, is accidentally deleted, or is viewed offline without the linked stylesheet, the entire website renders as unstyled plain text.
6) Disadvantage — Additional HTTP request and learning curve: Fetching a separate CSS file adds an initial HTTP request, and novice template users must understand both HTML and CSS syntax (and cascade specificity) to customize their site.

Mentor tip

(c)

3 marks

Explain how the TCP/IP protocol suite guarantees reliable downloading of the compressed template archive:
1) Packet segmentation and sequencing (TCP): TCP breaks the compressed archive into numbered packets and attaches headers containing sequence numbers and error-checking checksums.
2) Acknowledgements and retransmission (TCP): The receiving browser verifies each packet's checksum and sends an `ACK` signal back to the server; if a packet is corrupted or an `ACK` times out, TCP automatically retransmits the missing packet and reassembles them in exact sequence order.
3) Addressing and routing (IP): IP attaches destination and source IP addresses to route each packet across network hops to the correct client machine.

Mentor tip

Cover packet numbering/checksums, ACK acknowledgements with automatic retransmission of lost packets (TCP), and correct destination routing (IP).

(d)

4 marks

Evaluate lossy versus lossless compression when downloading the website template package (HTML, CSS, images, and sound effects):
1) Lossy compression mechanism and suitability: Permanently discards perceptually redundant data to achieve high compression ratios (much smaller file sizes and faster downloads); well suited for the template's web images (JPEG) and sound effects (MP3) where minor quality degradation is imperceptible.
2) Lossy limitation: Cannot be applied to text or code files because discarding bytes corrupts syntax.
3) Lossless compression mechanism and suitability: Compresses data using statistical redundancy (such as ZIP/GZIP) so the exact original bit-for-bit file is reconstructed upon decompression.
4) Synthesis for the template archive: Lossless compression is mandatory for packaging the HTML and CSS files (and the overall `.zip` archive) because even a single lost character would break the markup or stylesheet rules.

Mentor tip

Match lossy compression to the images/audio folders (smaller size, tolerable quality trade-off) and lossless compression to the HTML/CSS code files (exact bit-for-bit recovery required).

Question 8

16 marks

Open-source portal: server-side registration, third-party OAuth privacy, URL generation, and PHP string manipulation

Web science

(a)

4 marks

Evaluate the use of server-side scripting to handle user registration:
1) Advantage — Browser independence: Because the script executes on the web server and returns standard HTML, registration works reliably across all client browsers without requiring user plugins.
2) Advantage — Database integration and hidden logic: Server-side scripts connect directly to the backend user database on the server, keeping validation logic and database credentials hidden from client inspection.
3) Disadvantage — Network latency and server load: Every registration submission requires a network round-trip to the server, and high simultaneous registration traffic can bottleneck server CPU resources.
4) Disadvantage — Centralized security target: A vulnerability in the server-side script or server database could expose the central repository of registered user accounts.

Mentor tip

Weigh server-side advantages (browser independence, direct database access, hidden source code) against drawbacks (round-trip latency, server load).

(b)

4 marks

Explain how authenticating via an established third-party provider (e.g., OAuth / federated login) preserves user privacy:
1) Credential isolation: The user's sensitive password is never typed into or stored by `OpenSourceDev.org`; credentials are submitted directly to the trusted third-party identity provider over an encrypted connection.
2) Token-based verification: The third-party provider verifies the user's identity and returns only a cryptographic confirmation token (a yes/no verification and basic identifier) to the open-source portal.
3) Reduced exposure to breaches: Even if `OpenSourceDev.org` suffers a database breach, attackers cannot harvest user passwords or private social network profiles.
4) Minimal data footprint: The open-source website only stores the user's email address (for notifications) rather than accumulating sensitive personal authentication secrets.

Mentor tip

Explain that the third party verifies the password and returns a confirmation token, so `OpenSourceDev.org` never sees or stores the user's password.

(c)(i)

2 marks

Outline, with an example, how URLs for newly uploaded code resources are constructed:
1) Hierarchical path concatenation: Append the directory path and specific filename/identifier of the new code resource onto the base domain URL (`www.OpenSourceDev.org`).
2) Concrete example: `https://www.OpenSourceDev.org/releases/python/sort_module.py` (or `www.OpenSourceDev.org/newcode/script01.js`).

Mentor tip

Explain that the relative folder/file path is appended to the base domain name and provide a valid example URL.

(c)(ii)

3 marks

Outline the automated steps performed by the weekly notification script:
1) Query new resources: The script queries the server directory or database log to retrieve the list of new code URLs uploaded during the past week.
2) Compose message: It formats and inserts those generated URLs into an email notification body/template.
3) Dispatch to subscribers: It queries the registered users table for subscriber email addresses and dispatches the email batch via an SMTP mail server.

Mentor tip

State the three logical steps: fetch the list of new code URLs, embed them into an email template, and send to the list of registered subscriber emails.

(d)

3 marks

Trace the server-side PHP processing when `https://www.the2nd.org/bin.php?id=70` is submitted from IP `172.16.254.1`:
1) Form submission via POST: The HTML form sends `url = "https://www.the2nd.org/bin.php?id=70"` via HTTP `POST`; the script detects `REQUEST_METHOD == "POST"` and invokes `make_short($url)`.
2) String transformation trace inside `make_short()`:
- `make_alpha_string( $u) ‘ s t r i p s t h e p r o t oco l ‘ h ttp s ‘, t h es u b s t r in g ‘ w w w ‘, an d a l l n o n - l e tt er c ha r a c t er s (‘ : ‘, ‘/‘, ‘2‘, ‘.‘, ‘ ? ‘, ‘ = ‘, ‘7‘, ‘0‘), l e a v in g ‘$ x = "thendorgbinphpid"`.
- `first4_last4( $x) ‘ co n c a t e na t es t h e f i r s t 4 l e tt er s (‘" t h e n "‘) an d l a s t 4 l e tt er s (‘" h p i d "‘), y i e l d in g ‘$ y = "thenhpid"`.
- `limits( $x) ‘ co n c a t e na t es t h e f i r s tl e tt er (‘" t "‘) an d l a s tl e tt er (‘" d "‘), y i e l d in g ‘$ z = "td"`.
- Concatenating ` $y .".".$ z` produces `$short = "thenhpid.td"`.
3) Database insertion: The script executes `mysql_query` to insert the record triple `('https://www.the2nd.org/bin.php?id=70', 'thenhpid.td', '172.16.254.1')` into the `url_db` table.

Mentor tip

Carefully trace `$x = "thendorgbinphpid"` (removing `https`, `www`, digits `2`, `7`, `0`, and punctuation) to derive the exact shortened string `"thenhpid.td"` and the inserted database tuple.

Question 9

14 marks

Museum website redesign: static vs dynamic web pages, interactive services, PageRank, and SEO meta-tags

Web science

(a)

3 marks

Identify three differences between a static web page and a dynamic web page:
1) Content customization: A static page delivers the exact same fixed HTML content to every visitor, whereas a dynamic page generates customized content on the fly based on user queries or preferences.
2) Database and script integration: Dynamic pages execute server-side/client-side scripts and query backend databases to assemble content, whereas static pages consist solely of pre-written HTML files stored on the server.
3) Interactivity and updating: Dynamic pages allow interactive user input (search filters, booking forms) without manually editing HTML files, whereas updating a static page requires an administrator to rewrite and re-upload the HTML source code.

Mentor tip

Contrast fixed HTML views for all users (static) against script/database-driven personalized views and user interactivity (dynamic).

(b)

4 marks

Suggest two dynamic web services for the museum and state the benefit of each:
1) Service 1 — Online ticket booking and donation portal: Allows visitors to reserve timed entry tickets, book school tours, or make charitable donations online. Benefit: Generates direct funding revenue and improves visitor convenience by eliminating ticket queues.
2) Service 2 — Interactive searchable 3D virtual exhibition / downloadable audio guide: Enables global users to filter artefacts by historical era or preview exhibits virtually. Benefit: Dramatically increases public engagement, educational reach, and foot traffic to the physical museum.

Mentor tip

Pair each concrete dynamic feature (e.g., online ticket/donation checkout, interactive virtual tour) with a clear benefit addressing the museum's funding or visitor numbers.

(c)

4 marks

Explain how adding interactive online services improves the museum's search engine ranking:
1) Increased visitor traffic and dwell time: Interactive virtual tours and ticket portals attract more visitors and keep users engaged on the site longer.
2) Growth of authoritative inbound links (backlinks): External organizations (such as tourist boards, schools, universities, and local government portals) will link to the museum's interactive resources and booking pages.
3) PageRank / authority boost: Search engine ranking algorithms (like PageRank) weight incoming links from reputable external domains heavily as votes of authority.
4) Fresh indexed content: Frequent updates to events and dynamic exhibitions signal to web crawlers that the site is active and relevant, elevating its position in search results.

Mentor tip

Connect interactive services -> external links from tourist boards/schools (backlinks) + higher traffic -> higher PageRank score.

(d)

3 marks

Suggest how cataloguing museum artefacts with HTML `<meta>` tags improves Search Engine Optimization (SEO):
1) Explicit keyword and description metadata: `<meta name="keywords">` and `<meta name="description">` tags summarize each artefact's historical period, artist, and medium in the HTML `<head>`.
2) Accurate crawler indexing: When search engine spiders crawl the catalogue, they parse these meta-tags (alongside robot directives like `index, follow` and language tags) to classify and index each piece accurately in the search database.
3) Higher relevance matching and click-through: When users search for specific historical artefacts, the search engine matches their query against the indexed meta-keywords and displays the meta-description snippet, improving both ranking relevance and visitor click-through rates.

Mentor tip

Explain the three-step chain: meta-tags describe artefact keywords -> web crawlers read them to index the page -> search engines rank the page higher for matching user queries.

Option D: Object-oriented programming · Option

Questions 10–12 · 45 marks

Question 10

14 marks

Restaurant Payment and FoodItem classes: attribute initialization, static members, data types, and mutators

Object-oriented programming

(a)

2 marks

Outline how `fiCount` and `diCount` can be initialized to `0` without writing assignment statements inside the constructor:
1) Direct declaration initialization: Assign the initial value directly when declaring the instance variables at the top of the `Payment` class (`private int fiCount = 0;` and `private int diCount = 0;`).
2) Default Java primitive behaviour: Alternatively, in Java, numeric `int` instance variables are automatically initialized to `0` by default when an object is instantiated.

Mentor tip

Write `private int fiCount = 0;` in the class attribute declaration section outside the constructor.

(b)

2 marks

State the implication of the `static` keyword on variables (`foodTax`, `drinkTax`) and methods (`findPrice`) in the `Payment` class:
1) Class-level ownership: `static` attributes belong to the `Payment` class itself rather than to any individual `Payment` object, so a single shared copy exists in memory across all 50 restaurant tables.
2) Object-independent invocation: `static` methods (like `Payment.findPrice(...)` or `Payment.getFoodTax()`) can be invoked directly using the class name without instantiating a `Payment` object.

Mentor tip

Do not confuse `static` with `final` (`static` variables CAN be changed, but their value is shared across all instances of the class).

(c)

4 marks

Explain the benefits of choosing specific data types using two examples from `Payment` and `FoodItem`:
1) Example 1 — `double` for `foodTax` / prices vs `int` for `quantity` / `fiCount`: Declaring `foodTax` as `double` allows fractional decimal values (`0.2`) required for accurate financial tax calculations, whereas declaring `quantity` as `int` restricts item counts to whole numbers and uses less memory (32 bits vs 64 bits).
2) Example 2 — `String` for `itemCode` vs `FoodItem[]` array for `fi`: Declaring `itemCode` as `String` allows alphanumeric codes like `"f102"` that do not require arithmetic, while declaring `fi` as a `FoodItem[]` object array groups up to 100 ordered items under a single indexed identifier for easy loop processing.

Mentor tip

Give two concrete attribute examples from the code and explain the specific benefit (such as decimal precision, memory efficiency, or valid operations) of each type.

(d)

3 marks

Describe the purpose of the statement `private FoodItem[] fi = new FoodItem[100];`:
1) Array declaration and type: Declares an array reference variable named `fi` that holds elements of object type `FoodItem`.
2) Memory instantiation: Allocates memory space for a fixed maximum capacity of `100` `FoodItem` references.
3) Encapsulation: The `private` modifier restricts direct access so only methods inside the `Payment` class can read or modify the `fi` array.

Mentor tip

Cover all three parts of the statement: `private` (encapsulation), `FoodItem[] fi` (array of FoodItem objects), and `new FoodItem[100]` (capacity of 100).

(e)

3 marks

Construct the `addFoodItem(FoodItem f)` method in the `Payment` class to append a `FoodItem` and increment the counter:
```java
public void addFoodItem(FoodItem f) {
fi[fiCount] = f;
fiCount = fiCount + 1; // or fiCount++;
}
```

Mentor tip

Include the correct `public void` method header with a `FoodItem` parameter, store the parameter at index `fiCount`, and increment `fiCount`.

Question 11

18 marks

Tracing Payment driver code, accessor chaining, linear search findPrice(), and calculateBill()

Object-oriented programming

(a)

3 marks

Trace the three `System.out.println` statements in the driver code:
1) `tables[1].getFiCount()` -> Two `FoodItem` objects (`a` and `b`) were added to `tables[1]`: outputs `2`
2) `Payment.getFoodTax()` -> Returns the static `foodTax` value: outputs `0.2`
3) `tables[2].getDi(1).getItemCode()` -> Index `0` of `tables[2]`'s `di` array holds `c` (`"d102"`), and index `1` holds the second added `DrinkItem` (`"d103"`): outputs `d103`

Mentor tip

Remember Java arrays are 0-indexed, so `getDi(1)` retrieves the SECOND drink item added to `tables[2]` (`"d103"`).

(b)(i)

1 mark

Write a statement to print the number of drink items ordered by table 40:
```java
System.out.println(tables[40].getDiCount());
```

Mentor tip

Access `tables[40]` and invoke the `getDiCount()` accessor.

(b)(ii)

1 mark

Write a statement to print the item code of the third food item (index 2) ordered by table 2:
```java
System.out.println(tables[2].getFi(2).getItemCode());
```

Mentor tip

The third food item is at 0-based index `2`, so chain `getFi(2).getItemCode()` on `tables[2]`.

(c)

6 marks

Construct `findPrice(Item[] pl, String c)` in `Payment` using a loop with early exit to return the unit price of item code `c`:
```java
public static double findPrice(Item[] pl, String c) {
int i = 0;
double price = 0.0;
boolean found = false;
while (i < pl.length && !found) {
if (pl[i] != null && pl[i].getCode().equals(c)) {
price = pl[i].getPrice();
found = true;
}
i++;
}
return price;
}
```

Mentor tip

Use a `while` loop with a `boolean found` flag (or `return pl[i].getPrice();` early exit) and use `.getCode()` and `.getPrice()` accessors.

(d)

7 marks

Construct the `calculateBill(Item[] pl)` method in `Payment` to compute the total tax-inclusive bill for both food and drink items:
```java
public double calculateBill(Item[] pl) {
double total = 0.0;
for (int i = 0; i < fiCount; i++) {
String code = fi[i].getItemCode();
double unitPrice = findPrice(pl, code);
total = total + (fi[i].getQuantity() * unitPrice * (1.0 + foodTax));
}
for (int j = 0; j < diCount; j++) {
String code = di[j].getItemCode();
double unitPrice = findPrice(pl, code);
total = total + (di[j].getQuantity() * unitPrice * (1.0 + drinkTax));
}
return total;
}
```

Total = i = 0 \sum fiCount - 1 q_{i} p_{i} (1 + foodTax) + j = 0 \sum diCount - 1 q_{j} p_{j} (1 + drinkTax)

Mentor tip

Loop through `fi` up to `fiCount` (multiplying by `1 + foodTax`) and `di` up to `diCount` (multiplying by `1 + drinkTax`), calling `findPrice(pl, code)` for each item.

Question 12

13 marks

UML class relationships, team benefits of encapsulation, and inheritance across business units

Object-oriented programming

(a)

3 marks

Construct the UML class relationship diagram connecting `Payment`, `FoodItem`, `DrinkItem`, and `Item`:
1) Draw four class boxes labelled `Payment`, `FoodItem`, `DrinkItem`, and `Item`.
2) Draw a `'has a'` (aggregation/composition) arrow from `Payment` to `FoodItem` and another `'has a'` arrow from `Payment` to `DrinkItem` (since `Payment` contains arrays `fi` and `di`).
3) Draw a `'uses'` (dependency) arrow from `Payment` to `Item` (since `Payment.findPrice()` and `calculateBill()` take `Item[] pl` as a parameter).

Mentor tip

Clearly label the arrows from `Payment` to `FoodItem`/`DrinkItem` as 'has a' and the arrow from `Payment` to `Item` as 'uses'.

(b)

6 marks

Describe two benefits of encapsulation for the programming team, referencing the restaurant classes:
1) Benefit 1 — Data protection and prevented side-effects: Declaring attributes `private` (such as `private int quantity` in `FoodItem` or `private int fiCount` in `Payment`) prevents external classes from accidentally overwriting or corrupting internal object state.
2) Benefit 1 — Independent variable naming: Because attributes are locally scoped and hidden inside their class, different developers working on `FoodItem`, `DrinkItem`, and `Item` can freely reuse variable names like `code` or `quantity` without naming collisions.
3) Benefit 2 — Modularity and cohesive code organization: Bundling related data (`fi`, `di`, tax rates) and the methods that operate on them (`addFoodItem()`, `calculateBill()`) inside `Payment` creates a self-contained module.
4) Benefit 2 — Parallel team maintenance: One programmer can modify the internal implementation of `Payment.calculateBill()` without breaking code written by another team member in the driver class, provided the public method signatures remain unchanged.

Mentor tip

For each of the two benefits (data protection/scope isolation and modularity/maintainability), cite a specific class and attribute/method from the paper.

(c)

4 marks

Explain how inheritance improves design clarity and reduces code duplication across the company's restaurant, hotel, shop, and car hire businesses:
1) Superclass abstraction: Define a generic `Payment` (or `SaleItem`) superclass containing attributes and methods common to all business units (such as invoice date, customer ID, basic tax calculation, and total summation).
2) Subclass specialization: Create business-specific subclasses (`RestaurantPayment`, `HotelPayment`, `CarHirePayment`, or `FoodItem` / `DrinkItem` extending `MenuItem`) that inherit all shared superclass attributes and methods.
3) Code reduction: Shared billing and lookup code is written and tested only once in the superclass rather than being duplicated across four separate business programs.
4) Design clarity and overriding: The hierarchical structure clearly documents how business entities relate, while subclasses can add specialized fields (e.g., room number or rental days) and override `calculateBill()` if specific tax rules apply.

Mentor tip

Explain both how a superclass eliminates duplicated code across the businesses and how a clear hierarchy with method overriding improves design clarity.

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

Mentor insights

Traps to watch for

01
Databases: Art student examination relation: data vs information, validation · Q2
Define both terms and cite a specific value from `CLASS_TABLE` (such as `99` or `"Joe Skrin"`) to illustrate the difference.
02
Modelling and simulation: Weather forecasting simulations: supercomputing advances, chaos/l · Q6
Provide two distinct factors (e.g., faster supercomputers allowing finer grid resolution, and richer satellite/sensor input data) and explain each.
03
Web science: Open-source portal: server-side registration, third-party OAuth p · Q8
Weigh server-side advantages (browser independence, direct database access, hidden source code) against drawbacks (round-trip latency, server load).
04
Object-oriented programming: Tracing Payment driver code, accessor chaining, linear search fin · Q11
Remember Java arrays are 0-indexed, so `getDi(1)` retrieves the SECOND drink item added to `tables[2]` (`"d103"`).

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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