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Worked solutions

IB Computer Science SL · Paper 2

Computer Science, Standard Level

Session: May 2018
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 May 2018 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

Galaxy Bank relational database design, query construction, and concurrency

Databases

(a)

2 marks

Identify the entities and cardinality requirements from the scenario:
A Bank Branch hosts multiple Customers (1-to-many relationship).
A Customer can hold multiple Loans (1-to-many relationship).
Construct the Entity-Relationship Diagram (ERD) structure:
BRANCH (1) ----< (has / maintains) >---- (M) CUSTOMER (1) ----< (holds / takes out) >---- (M) LOAN

Mentor tip

Ensure both 1:N relationship links are clearly directed from Branch to Customer and Customer to Loan.

(b)

2 marks

Examine the query conditions: Amount > 600000 AND (Type = 'Home' OR Type = 'Venture').
Filter potential rows from LOANS:
1) RD050789: Customer 987887982, Amount 430,000,000, Type Venture -> Matches criteria (430M > 600K).
2) RG903540: Customer 124567552, Amount 231,900,000, Type Venture -> Matches criteria (231.9M > 600K).
3) XY348801: Customer 648782904, Amount 800,000, Type Home -> Matches criteria (800K > 600K).
Format the query result table:
RD050789 | 987887982 | 430000000 | Venture
RG903540 | 124567552 | 231900000 | Venture
XY348801 | 648782904 | 800000 | Home

Mentor tip

Carefully filter out XY080911 (500,000 is not > 600,000) and ED569891 (Education type does not match Home or Venture).

(c)

4 marks

Outline the algorithmic steps to produce the required output:
Step 1: Perform an equi-join between CUSTOMERS and ACCOUNTS on Customer_ID (e.g. CUSTOMERS.Customer_ID = ACCOUNTS.Customer_ID).
Step 2: Filter merged records by applying the conditional predicate Balance > 300000.
Step 3: Project the Family_name attribute (and optionally Acct_no / Balance) from the filtered relation.
Step 4: Output or return the resulting set of family names.

Mentor tip

Explicitly identify the two tables, the join condition on the common foreign key, the numerical condition, and the projected attribute.

(d)

3 marks

Explain role-based access control (RBAC):
1) The DBMS assigns granular permission levels to different categories of users (e.g. customers, tellers, DBAs).
2) Customers are restricted to read-only access for their own personal accounts and loan portfolios, preventing visibility into other patrons' records.
3) Elevated administrative privileges are reserved strictly for system operations, safeguarding confidential financial data against unauthorized inspection or modification.

Mentor tip

Connect user privilege levels directly to preventing unauthorized viewing of sensitive financial balances.

(e)

3 marks

Explain the role of row locking in transaction processing:
1) Row locking places an exclusive lock on an individual record whenever an active transaction begins modifying it.
2) Concurrent transactions attempting to modify the exact same row are queued or suspended until the first transaction commits or rolls back.
3) This eliminates race conditions, lost updates, and dirty reads, thereby maintaining ACID data consistency across the banking system.

Mentor tip

Explain that row-level locks prevent simultaneous writes without having to lock the entire table, preserving concurrency.

Question 2

12 marks

Theatre booking update anomalies, backup/recovery, and DBA administration

Databases

(a)

2 marks

Identify two types of update anomalies:
1) Insertion anomaly: Inability to add valid information (e.g. a new show or actor) without also creating an artificial or dummy booking record.
2) Deletion anomaly: Deleting an existing booking record inadvertently deletes unique entity data (e.g. removing the last booking for a performance erases all show metadata).
3) Modification anomaly: Inconsistent updates across duplicate rows when an attribute changes in one tuple but remains unchanged in others.

Mentor tip

State any two of insertion anomaly, deletion anomaly, or modification anomaly with a clear description.

(b)

4 marks

Method 1: Transaction log replay (Roll-forward recovery):
Restore the most recent periodic full backup image, then apply sequential changes recorded in the transaction redo log up to the moment immediately preceding corruption.
Method 2: Rollback / Backward recovery (Undo logging):
When an active transaction crashes mid-execution, read uncommitted states from the transaction undo log and reverse all partial writes, returning the database to a consistent checkpoint.

Mentor tip

Describe two distinct mechanisms: roll-forward from backup logs and transaction rollback/undo.

(c)

3 marks

Identify three key duties performed by a Database Administrator (DBA):
1) Database schema design, maintenance, and performance tuning (e.g. creating indexes, managing storage, query optimization).
2) Security and user permission management (configuring user accounts, password policies, access rights, and authentication).
3) Disaster recovery management (scheduling routine backups, verifying backup integrity, executing restoration drills).

Mentor tip

Pick three clear administrative responsibilities: performance/indexing, access rights/security, and backup/recovery.

(d)

3 marks

Describe data masking / pseudonymisation techniques:
1) The DBA can replace real credit card numbers and personal identifiers with synthetic tokens or hash values in operational tables.
2) Dynamic data masking hides all but the final four digits of payment cards (e.g. 'XXXX-XXXX-XXXX-1234') when queried by general staff.
3) Sensitive cardholder tables are encrypted at rest with decryption keys restricted from non-essential third-party services.

Mentor tip

Focus on pseudonymisation, data masking (tokenisation), or column-level encryption with restricted views.

Question 3

19 marks

Music department database normalisation to 3NF and data integrity

Databases

(a)

3 marks

Explain one major benefit of database normalisation:
1) Elimination of redundant data: Each piece of factual information is stored in exactly one logical location.
2) Prevention of update anomalies: Updating an entity's attribute (such as a school's contact number) requires changing only a single row in the parent table.
3) Storage optimization and referential integrity: Tables occupy less disk space and maintain consistency through relational foreign keys.

Mentor tip

Focus on removing redundancy and eliminating the risk of data inconsistency during updates.

(b)

3 marks

Identify three validation or integrity rules for the School_phone_no attribute:
1) Length check: Restrict the field to exactly 9 characters (or standard international phone length).
2) Format / Pattern check: Enforce an input mask permitting only digits and valid separators (e.g. regex `^[0-9]{9}$`).
3) Type / Character check: Disallow alphabetic and special characters, ensuring every input character is numeric.

Mentor tip

Specify concrete validation checks: length check, type check (digits only), and format check (input mask).

(c)

2 marks

Requirements to achieve 1st Normal Form (1NF):
1) Ensure all attributes hold atomic (indivisible) values: multi-valued entries such as `Student_Choice` (e.g. 'VIOLIN, PERCUSSION') and `School_phone_no` must be split so each cell holds a single value.
2) Establish a primary key that uniquely identifies each row without repeating groups.

Mentor tip

Atomicity is the essential keyword: eliminate repeating groups and multi-valued composite cells.

(d)

8 marks

Decompose the unnormalised structure through 1NF, 2NF, and 3NF:
1) STUDENT Table:
STUDENT (Student_ID [PK], First_Name, Family_Name, Date_of_Birth, School_ID [FK])
2) SCHOOL Table (eliminating transitive dependencies on School_Post_Code and School):
SCHOOL (School_ID [PK], School_Name, School_Post_Code)
3) SCHOOL_PHONE Table (handling multiple telephone numbers per school):
SCHOOL_PHONE (School_ID [PK, FK], Phone_Number [PK])
4) INSTRUMENT Table:
INSTRUMENT (Instrument_ID [PK], Instrument_Name)
5) STUDENT_INSTRUMENT Table (resolving M:N relationship between Students and Instruments):
STUDENT_INSTRUMENT (Student_ID [PK, FK], Instrument_ID [PK, FK])

Mentor tip

Make sure composite keys and foreign keys are explicitly marked to link students, schools, phones, and instruments without redundancy.

(e)

3 marks

Distinguish between 2NF and 3NF:
1) 2nd Normal Form (2NF) requires 1NF plus the removal of partial dependencies: every non-key attribute must depend on the whole primary key, not a proper subset of a composite key.
2) 3rd Normal Form (3NF) requires 2NF plus the removal of transitive dependencies: non-key attributes must depend solely on the primary key and never on another non-key attribute.
3) Summary axiom: 'Every non-key attribute must depend on the key, the whole key, and nothing but the key'.

Mentor tip

Contrast partial functional dependency (2NF) with transitive functional dependency (3NF).

Option B: Modelling and simulation · Option

Questions 4–6 · 45 marks

Question 4

18 marks

Ralph second-hand retail pricing model and spreadsheet testing

Modelling and simulation

(a)

4 marks

Specify suitable data types and ranges for the item attributes:
1) Item Type: String / Enumerated type {'furniture', 'lamp', 'musical instrument'}.
2) Brand Recognition: Integer in the range [1, 3] (1 = low, 2 = medium, 3 = high).
3) Condition: String / Enumerated type {'very good', 'good', 'fair'}.
4) Dimensions / Volume: Real (floating point) number $\geq 0$ dm $^{3}$ .

Mentor tip

State both the programmatic data type (String, Integer, Float) and the allowable discrete range for each variable.

(b)(i)

4 marks

Formulate the business rules determining the purchase decision:
Calculate estimated retail value based on brand multiplier, condition weight, and type.
If Estimated Value > 90 AND Purchase Price <= 0.40 * Estimated Value, purchase the item.
If Estimated Value <= 90 OR repair cost exceeds projected markup margin, decline purchase.

Mentor tip

Express rules clearly using logical conditions linking item value, purchase price, and profitability.

(b)(ii)

2 marks

Identify two items that yield a calculated value above 90:
Item 1: High-brand recognized antique furniture in 'very good' condition (e.g. brand = 3, condition = 'very good').
Item 2: Professional musical instrument with medium/high brand status in 'very good' condition (e.g. a branded violin with brand = 2 or 3).

Mentor tip

Choose combinations with brand >= 2 and condition 'very good' to guarantee a valuation > 90.

(c)

2 marks

Calculate the valuation adjustment for damaged goods:
Apply a percentage penalty deduction to the baseline valuation:
Base value $= 100$ , Damage factor reduction $= 30%$ :
$Adjusted Value = 100 \times (1 - 0.30) = 70$
State the revised selling price reflecting the repair overhead and reduced marketability.

Final Price = Base Value \times (1 - Penalty Rate)

Mentor tip

Show numerical steps clearly: subtract the percentage penalty from the base valuation.

(d)

4 marks

Construct an algorithm or formula to compute final selling price:
1) Determine base price from item lookup table based on category and volume.
2) Multiply by brand recognition factor ( $1.0, 1.25, 1.50$ ).
3) Apply condition coefficient (e.g. $1.0$ for 'very good', $0.75$ for 'good', $0.50$ for 'fair').
4) Add standard repair expenses and required profit margin ( $25%$ markup):
$Selling Price = (Base \times Brand \times Condition + Repair) \times 1.25$

Price = (V_{base} \cdot M_{brand} \cdot C_{cond} + Repair) \times (1 + Markup)

Mentor tip

Present a structured formula accounting for condition, brand multiplier, and business profit margin.

(e)

2 marks

Design two test cases for the model verification:
Test 1 (Boundary / Normal test): Input an item with maximum brand rating (3) and 'very good' condition to confirm pricing scales up correctly.
Test 2 (Erroneous / Extreme test): Input invalid brand values (e.g. brand = 0 or 5) or negative repair costs to verify error trapping and validation handling.

Mentor tip

Select one normal/boundary test and one erroneous/extreme data test.

Question 5

19 marks

Bakery queuing simulation, spatial modelling, and validation

Modelling and simulation

(a)

4 marks

Identify the core system variables in the bakery queuing model:
1) Customer arrival rate $λ$ (modelled using a Poisson distribution).
2) Service duration per customer $μ$ (time required to select, prepare, and pay for bread rolls).
3) Number of active servers / staff members ( $n = 2$ ).
4) Queue capacity and physical waiting area footprint.

Mentor tip

Specify arrival rate, service rate, server count, and shop floor spatial constraints.

(b)

3 marks

Explain why a discrete-event simulation is appropriate:
1) The state of the system changes only at discrete points in time when events occur (e.g. a customer arrives, order preparation finishes, a customer departs).
2) Time jumps between successive event occurrences rather than advancing in infinitesimal continuous increments.
3) This enables tracking queue lengths and idle staff intervals efficiently without wasteful continuous numerical integration.

Mentor tip

Link discrete events (arrival, order completed, departure) to system state transitions.

(c)

3 marks

Explain how customer balking / reneging is incorporated:
1) Define a threshold waiting queue length $L_{m a x}$ based on shop floor space.
2) When an arriving customer observes a queue length $\geq L_{m a x}$ , they leave immediately without joining the queue (balking).
3) Record balked customers as lost sales to assess revenue loss resulting from shop size bottlenecks.

Mentor tip

Explain balking when physical capacity is reached and note its impact on lost revenue.

(d)

3 marks

Explain the role of pseudorandom number generators in stochastic simulation:
1) Real customer arrivals and transaction durations vary unpredictably throughout the day.
2) Pseudorandom generation maps uniform values $U (0, 1)$ to service time probability distributions (e.g. exponential or normal).
3) Repeated simulation runs using different random seeds capture variance and generate realistic confidence intervals for peak waiting times.

Mentor tip

Focus on modelling variability in customer arrival intervals and service times.

(e)

6 marks

Propose a verification and validation strategy for the bakery model:
1) Model Verification (Building the model right):
- Trace simulation logic through structured code walkthroughs.
- Verify that under zero arrival rate queue remains zero, and under deterministic inputs outputs match analytical queuing equations ( $M / M /2$ ).
2) Model Validation (Building the right model):
- Gather empirical baseline data by timing actual customer arrivals and service times over several business days.
- Compare simulation output metrics (mean queue length, average wait time) against observed real-world measurements.
- Perform sensitivity analysis by varying parameters to ensure the model responds realistically.

Mentor tip

Clearly separate verification (internal code and mathematical correctness) from validation (comparison with real-world empirical data).

Question 6

8 marks

Automotive ECU sensor processing, control loop latency, and fail-safe operation

Modelling and simulation

(a)(i)

2 marks

State the role of the ECU feedback loop:
1) Continuously poll input sensors (e.g. wheel speed, engine temperature, oxygen levels) via ADC converters.
2) Compare sensed values against target reference thresholds and output corrective actuation signals (e.g. fuel injection, brake pressure) in real time.

Mentor tip

Describe the closed-loop cycle: sense input, compare with setpoint, trigger actuators.

(a)(ii)

2 marks

Explain the consequence of processing latency in vehicle control:
1) Delays in processing sensor readings result in delayed actuator responses (e.g. anti-lock braking modulation).
2) In safety-critical situations at high vehicle speeds, excessive latency can cause control instability, wheel lockup, or increased braking distance.

Mentor tip

Connect latency directly to vehicle instability or prolonged stopping distance during sudden braking.

(b)

4 marks

Describe a fail-safe mechanism in an automotive electronic control unit:
1) Sensor validation check: The ECU monitors sensor health using out-of-range checks and redundant cross-sensor voting.
2) Fail-safe transition: If a sensor produces aberrant or disconnected signals, the system flags a diagnostic trouble code (DTC) and transitions to a degraded 'limp-home' mode.
3) Actuator default: Safety actuators fall back to a mechanical default (e.g. passive hydraulic braking) to maintain driver control without catastrophic failure.

Mentor tip

Explain fault detection, entering a limp-home mode, and defaulting to a safe mechanical state.

Option C: Web science · Option

Questions 7–9 · 45 marks

Question 7

14 marks

Online banking web architecture, browser compatibility, and HTTPS security

Web science

(a)

2 marks

Distinguish between the Internet and the World Wide Web:
1) The Internet is the global hardware infrastructure of interconnected computer networks, routers, and transmission media operating over the TCP/IP suite.
2) The World Wide Web (WWW) is an information-sharing service built on top of the Internet, utilizing HTTP/HTTPS protocols to retrieve and render interlinked hypertext documents.

Mentor tip

Characterize the Internet as the physical network infrastructure and the Web as an application service running on it.

(b)

4 marks

Explain how web standards enable cross-browser compatibility:
1) Web standards defined by the W3C (HTML5, CSS, ECMAScript) provide universal specifications for markup rendering and script execution.
2) All compliant browsers parse standardized HTML/CSS DOM trees and execute JavaScript consistently regardless of underlying vendor engine (Blink, Gecko, WebKit).
3) Server-side banking applications deliver standard RESTful data payloads and standard markup, preventing proprietary client-side incompatibilities.

Mentor tip

Emphasize W3C open standards compliance for HTML, CSS, and ECMAScript across different browser engines.

(c)

2 marks

State two security benefits of HTTPS over HTTP:
1) End-to-end encryption: All request headers, cookies, and transaction payloads are encrypted using TLS/SSL, preventing eavesdropping and packet sniffing.
2) Server authentication and data integrity: Digital certificates issued by trusted Certificate Authorities verify server identity and guarantee that banking data is not altered in transit.

Mentor tip

Highlight encryption (confidentiality) and digital certificates (authentication/integrity).

(d)

3 marks

Explain the function of digital certificates in online banking sessions:
1) The bank's web server presents an X.509 digital certificate containing its public key signed by a reputable Certificate Authority (CA).
2) The user's browser verifies the CA signature against its pre-installed root trust store to confirm the domain belongs to the genuine bank.
3) The client encrypts a symmetric session key using the bank's public key during the TLS handshake, establishing a secure shared secret.

Mentor tip

Explain the role of the Certificate Authority, public key exchange, and preventing man-in-the-middle impersonation.

(e)

3 marks

Explain why client-side scripts alone are insufficient for banking security:
1) Client-side scripts execute in an untrusted environment where tech-savvy users can inspect, bypass, or alter JavaScript validation using browser developer tools.
2) Malicious actors can forge HTTP POST requests directly to banking endpoints without running client scripts.
3) Robust security requires authoritative server-side validation, session authentication, and parameterized query execution for every incoming transaction.

Mentor tip

Emphasize that client-side code can be modified or completely bypassed by an attacker; server validation is mandatory.

Question 8

15 marks

Sports knowledge platform, caching mechanisms, and web search indexing

Web science

(a)

3 marks

Explain how web proxy caching improves website performance:
1) A caching proxy stores copies of frequently requested static assets (images, CSS, media articles) closer to end users.
2) Subsequent client requests for cached assets are served locally by the proxy without traversing the wide area network back to the origin server.
3) This dramatically reduces page load latency, conserves bandwidth, and offloads processing stress from the primary web server.

Mentor tip

Connect local storage of resources to reduced latency and origin server workload relief.

(b)(i)

1 mark

Identify the purpose of a web crawler (spider):
An automated script that systematically traverses hyperlinks across the web to discover and download web pages for search engine indexing.

Mentor tip

State clearly that crawlers traverse hyperlinks to discover and retrieve web pages for index creation.

(b)(ii)

3 marks

Describe how an inverted index organizes sports knowledge documents:
1) During indexing, text is tokenized into distinct keyword stems (e.g. 'marathon', 'hydration').
2) The inverted index maps each unique word to a posting list containing document IDs and term occurrence frequencies.
3) When a user searches for multiple terms, the engine performs fast set intersections across posting lists instead of scanning raw document texts.

Mentor tip

Explain the mapping from keywords/terms to lists of document identifiers where they appear.

(c)

4 marks

Explain how PageRank evaluates page importance:
1) PageRank treats an inbound hyperlink from Page A to Page B as a vote of confidence in Page B's quality.
2) A link from a page with high authority (high PageRank) contributes significantly more weight than a link from an obscure page.
3) The authority passed by a page is divided by its total number of outbound links, preventing link-spam dilution.
4) A damping factor $d \approx 0.85$ models the probability of a user continuing to follow links rather than navigating elsewhere.

P R (u) = \frac{1 - d}{N} + d v \in B_{u} \sum \frac{P R ( v )}{L ( v )}

Mentor tip

Highlight inbound link count, incoming page authority, outbound link division, and the damping factor.

(d)

4 marks

Explain two search engine optimization (SEO) techniques for RunAndBeyond:
Technique 1 (Semantic metadata and structured markup): Incorporate meaningful `<title>`, `<meta description>`, and Schema.org semantic tags so search bots accurately classify sports guides.
Technique 2 (High-quality content and authoritative backlink building): Produce verified, in-depth athletic training literature that encourages organic external citations from sports federations and universities.

Mentor tip

Provide two clear SEO practices: on-page structured metadata and off-page backlink cultivation.

Question 9

16 marks

Mobile web application architecture, offline storage, and cloud synchronization

Web science

(a)(i)

3 marks

Outline how a progressive web application (PWA) operates on mobile devices:
1) The application is developed with standard responsive web technologies (HTML5, CSS, JS) that adapt dynamically to any screen form factor.
2) Service workers run as background threads, intercepting network requests to serve cached assets when offline.
3) A web app manifest enables users to install the web app directly onto their home screen with an app icon without downloading from an app store.

Mentor tip

Mention service workers, responsive layouts, and home screen installation via manifest.

(a)(ii)

2 marks

State two advantages of mobile web apps compared to native mobile applications:
1) Cross-platform code maintainability: A single responsive codebase runs across Android, iOS, and desktop browsers, reducing engineering costs.
2) Instant deployment: Updates published to the web server become immediately accessible to all users without requiring app store approval cycles.

Mentor tip

Focus on cross-platform portability from a single codebase and bypassing app store submission delays.

(b)(i)

2 marks

Identify two local client-side storage mechanisms:
1) IndexedDB: A client-side transactional object-oriented database capable of holding large structured data collections.
2) Web Storage API (localStorage): Key-value string storage suitable for lightweight session preferences and user profiles.

Mentor tip

Name IndexedDB and localStorage (or Cache API) with their roles.

(b)(ii)

5 marks

Describe the synchronization protocol between mobile client storage and central cloud database:
1) Offline data queuing: User actions completed while offline are written locally with universal unique identifiers (UUIDs) and generation timestamps.
2) Connection detection: A network event listener detects the restoration of Internet connectivity.
3) Batch transmission: The client issues HTTPS background POST requests sending the queued transactions to the cloud REST API.
4) Conflict resolution: The server checks timestamps and record version vectors; in case of concurrent edits, it applies a designated resolution policy (e.g. latest timestamp wins or 3-way merge).
5) Acknowledgement and state update: The server confirms successful persistence, prompting the local client to purge the sync queue.

Mentor tip

Walk through the sequence: local queuing, reconnection detection, batch sync, conflict handling (timestamps), and queue clearance.

(c)

4 marks

Evaluate copyright and ethical challenges of content scraping on the web:
1) Intellectual property infringement: Automated scraping reproduces proprietary sports journalism and training datasets without licensing or attribution, depriving creators of ad revenue.
2) Server resource abuse: Aggressive crawlers can flood independent web servers with excessive concurrent requests, degrading performance for human visitors (denial of service).
3) Fair use and terms of service: Web platforms often explicitly prohibit unauthorized extraction in their robots.txt and terms of use, creating legal liabilities for data aggregators.

Mentor tip

Balance intellectual property/revenue loss against technical server load and terms-of-service violations.

Option D: Object-oriented programming · Option

Questions 10–12 · 45 marks

Question 10

13 marks

Hotel loyalty scheme Points class modifiers, constructor overloading, and status query

Object-oriented programming

(a)

4 marks

Outline how access modifiers affect variable access using two non-private examples:
1) `public`: The variable or method is accessible from any other class within the entire application, enabling open access but removing encapsulation.
2) `protected`: The variable is accessible within its own package and by subclasses inheriting from it, supporting extensible class hierarchies while preventing external exposure.
3) Package-private (default): The variable is accessible only to classes residing within the same package.

Mentor tip

Explain public and protected (or package-private), highlighting the difference in scope and inheritance accessibility.

(b)

4 marks

Explain constructor overloading in the Points class:
1) The OOP feature is constructor overloading (a form of compile-time / static polymorphism).
2) Both constructors share the exact same identifier (`Points`) but possess distinct parameter signatures: `Points(String id)` vs `Points(String id, int bp)`.
3) At instantiation, the compiler determines which constructor to execute by evaluating the number and types of arguments provided in the `new` expression.

Mentor tip

Name constructor overloading and explain how distinct parameter lists allow the compiler to bind the appropriate constructor.

(c)

1 mark

Calculate Tim's total points and determine his 2019 status:
Bonus points allocated $= 1000$ .
Total stay duration $= 2 + 1 + 6 = 9 days$ .
Stay points $= 9 \times 1000 = 9000 points$ .
Total points accumulated $= 1000 + 9000 = 10000 points$ .
Status rule: Silver threshold is 10,000 or more but less than 50,000 points.
Tim is assigned: Silver

Total = 1000 + (2 + 1 + 6) \times 1000 = 10000 ⟹ Silver

Mentor tip

Show total calculation: 1000 bonus + 9000 stay points = 10000 points, which meets the 10,000 Silver threshold.

(d)

1 mark

State how an individual object is accessed in the array:
By referencing the array identifier followed by the zero-based integer index enclosed in square brackets, e.g. `allPoints[i]`.

Mentor tip

State that access is achieved using the array index in square brackets.

(e)

3 marks

Construct the `isGold()` method in Java:
```java
public boolean isGold()
{
return statusNow.equalsIgnoreCase("Gold");
}
```
Explanation: The method checks whether the current member's status string equals 'Gold' and returns a boolean flag.

Mentor tip

Use a boolean return type and compare statusNow to 'Gold' using .equals() or .equalsIgnoreCase().

Question 11

25 marks

Hotel Visits class UML, trace output, and points calculation algorithms

Object-oriented programming

(a)

3 marks

Construct the UML diagram for the Visits class:
+------------------------------------------+
| Visits |
+------------------------------------------+
| - hotelCode : String |
| - days : int |
+------------------------------------------+
| + Visits(h : String, d : int) |
| + getDays() : int |
+------------------------------------------+
Key conventions: '-' indicates private attributes, '+' indicates public methods, and types follow colons.

Mentor tip

Draw three distinct boxes with class name, private attributes (-), and public methods (+) with parameter types.

(b)(i)

1 mark

Trace `allPoints[2].getMemberId()`:
`allPoints[2]` was instantiated as `new Points("m102", 2000)`.
Output: m102

Mentor tip

Output is simply the string literal 'm102'.

(b)(ii)

1 mark

Trace `allPoints[0].getBonusPoints()`:
`allPoints[0]` was instantiated using `new Points("m100")` (single argument constructor), which sets `bonusPoints = 0`.
Output: 0

Mentor tip

The 1-arg constructor initializes bonusPoints to 0.

(b)(iii)

1 mark

Trace `allPoints[1].getAllVisits(1).getDays()`:
`allPoints[1]` added `v1` (3 days) at index 0, and `new Visits("h004", 6)` at index 1.
Output: 6

Mentor tip

Visit at index 1 for allPoints[1] has days = 6.

(c)

5 marks

Construct `calculateTotalPoints()` in the Points class:
```java
public int calculateTotalPoints()
{
int totalStayDays = 0;
for (int i = 0; i < y; i++)
{
totalStayDays += allVisits[i].getDays();
}
totalPoints = bonusPoints + (totalStayDays * 1000);
return totalPoints;
}
```
Algorithm: Loop from 0 up to the visit count `y`, accumulate days from each visit via `getDays()`, multiply by 1000, add bonus points, and return the sum.

Mentor tip

Iterate strictly up to y (the number of visits logged) rather than allVisits.length to prevent NullPointerException.

(d)

7 marks

Construct `daysMissing()` in the Points class:
```java
public int daysMissing()
{
int currentEarned = calculateTotalPoints();
int requiredPoints = 0;
if (statusNow.equalsIgnoreCase("Gold"))
{
requiredPoints = 50000;
}
else if (statusNow.equalsIgnoreCase("Silver"))
{
requiredPoints = 10000;
}
else
{
return 0; // Bronze has no minimum point requirement
}
int deficit = requiredPoints - currentEarned;
if (deficit <= 0)
{
return 0;
}
int days = deficit / 1000;
if (deficit % 1000 != 0)
{
days++;
}
return days;
}
```
Explanation: Determine threshold for maintaining statusNow (50,000 for Gold, 10,000 for Silver, 0 for Bronze). Calculate remaining deficit and convert points into integer days needed.

Mentor tip

Handle Bronze as requiring 0 extra days, and ensure that if currentEarned exceeds requiredPoints the method returns 0.

(e)

4 marks

Suggest how the hotel chain can leverage inheritance:
1) Define an abstract superclass `Status` (or `Member`) containing common attributes (memberId, totalPoints, discountRate) and shared methods.
2) Subclasses `GoldMember`, `SilverMember`, and `BronzeMember` inherit from `Status`.
3) Subclasses can override methods such as `applyPerks()` or `calculateBonus()` to provide tier-specific services (e.g. complimentary room upgrades for Gold, late checkout for Silver) without duplicating shared member management code.

Mentor tip

Propose a superclass with common behavior and specialized subclasses overriding benefit methods.

(f)

3 marks

Identify three changes required at annual reset (midnight 31 December):
1) Update member status: Assign `statusNow = statusNextYear;` for all existing members.
2) Reset annual counters: Reset `totalPoints = 0;` and reset the visit counter `y = 0;` for the new operating year.
3) Clear bonus points and visit arrays: Reset `bonusPoints = 0;` (as bonus points apply for the joining year only) and re-instantiate `allVisits = new Visits[366];`.

Mentor tip

Name the three rollover steps: shift statusNextYear into statusNow, reset visit counter y and totalPoints, and clear single-year bonus points.

Question 12

7 marks

Hotel visit analysis algorithm across parallel customer stay history

Object-oriented programming

7 marks

Outline the algorithmic steps to find the hotel with the most customer days:
Step 1: Retrieve the customer's `Points` object from `allPoints` using their `memberId`.
Step 2: Maintain two parallel arrays (or a Hash Map / frequency table) `hotelCodes[]` and `totalDays[]` to track aggregated stay durations per hotel.
Step 3: Loop through all visits of the customer from `0` to `y - 1` using `getAllVisits(i)`.
Step 4: For each visit, extract `hotelCode` and `days`. Search `hotelCodes[]`:
- If `hotelCode` exists, add `days` to the matching index in `totalDays[]`.
- Otherwise, append `hotelCode` to `hotelCodes[]` and set `totalDays` to `days`.
Step 5: Perform a linear scan over `totalDays[]` to identify the maximum day count and note the corresponding `hotelCode`.
Step 6: Query the `Hotel` collection to find the `Hotel` object whose ID matches the identified `hotelCode` and retrieve its name attribute.
Step 7: Output or return the resulting hotel name.

Mentor tip

Clearly describe aggregating days per unique hotelCode across all customer visits, locating the maximum total, and looking up the hotel name.

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
Inadvertent inclusion of non-matching loan amounts · Q1
The SQL query requires Amount > 600000. An amount of exactly 500000 or lower must be excluded even if the type matches Home.
02
Confusing 2NF partial dependencies with 3NF transitive dependencies · Q3
2NF eliminates functional dependencies on a part of a composite primary key, whereas 3NF eliminates functional dependencies between non-key attributes.
03
Looping past active visits in array · Q11
The allVisits array has length 366, but only y elements contain instantiated Visit objects. Iterating to allVisits.length causes a NullPointerException.

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 2018
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 May 2018 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

Galaxy Bank relational database design, query construction, and concurrency

Databases

(a)

2 marks

Identify the entities and cardinality requirements from the scenario:
A Bank Branch hosts multiple Customers (1-to-many relationship).
A Customer can hold multiple Loans (1-to-many relationship).
Construct the Entity-Relationship Diagram (ERD) structure:
BRANCH (1) ----< (has / maintains) >---- (M) CUSTOMER (1) ----< (holds / takes out) >---- (M) LOAN

Mentor tip

Ensure both 1:N relationship links are clearly directed from Branch to Customer and Customer to Loan.

(b)

2 marks

Examine the query conditions: Amount > 600000 AND (Type = 'Home' OR Type = 'Venture').
Filter potential rows from LOANS:
1) RD050789: Customer 987887982, Amount 430,000,000, Type Venture -> Matches criteria (430M > 600K).
2) RG903540: Customer 124567552, Amount 231,900,000, Type Venture -> Matches criteria (231.9M > 600K).
3) XY348801: Customer 648782904, Amount 800,000, Type Home -> Matches criteria (800K > 600K).
Format the query result table:
RD050789 | 987887982 | 430000000 | Venture
RG903540 | 124567552 | 231900000 | Venture
XY348801 | 648782904 | 800000 | Home

Mentor tip

Carefully filter out XY080911 (500,000 is not > 600,000) and ED569891 (Education type does not match Home or Venture).

(c)

4 marks

Outline the algorithmic steps to produce the required output:
Step 1: Perform an equi-join between CUSTOMERS and ACCOUNTS on Customer_ID (e.g. CUSTOMERS.Customer_ID = ACCOUNTS.Customer_ID).
Step 2: Filter merged records by applying the conditional predicate Balance > 300000.
Step 3: Project the Family_name attribute (and optionally Acct_no / Balance) from the filtered relation.
Step 4: Output or return the resulting set of family names.

Mentor tip

Explicitly identify the two tables, the join condition on the common foreign key, the numerical condition, and the projected attribute.

(d)

3 marks

Explain role-based access control (RBAC):
1) The DBMS assigns granular permission levels to different categories of users (e.g. customers, tellers, DBAs).
2) Customers are restricted to read-only access for their own personal accounts and loan portfolios, preventing visibility into other patrons' records.
3) Elevated administrative privileges are reserved strictly for system operations, safeguarding confidential financial data against unauthorized inspection or modification.

Mentor tip

Connect user privilege levels directly to preventing unauthorized viewing of sensitive financial balances.

(e)

3 marks

Explain the role of row locking in transaction processing:
1) Row locking places an exclusive lock on an individual record whenever an active transaction begins modifying it.
2) Concurrent transactions attempting to modify the exact same row are queued or suspended until the first transaction commits or rolls back.
3) This eliminates race conditions, lost updates, and dirty reads, thereby maintaining ACID data consistency across the banking system.

Mentor tip

Explain that row-level locks prevent simultaneous writes without having to lock the entire table, preserving concurrency.

Question 2

12 marks

Theatre booking update anomalies, backup/recovery, and DBA administration

Databases

(a)

2 marks

Identify two types of update anomalies:
1) Insertion anomaly: Inability to add valid information (e.g. a new show or actor) without also creating an artificial or dummy booking record.
2) Deletion anomaly: Deleting an existing booking record inadvertently deletes unique entity data (e.g. removing the last booking for a performance erases all show metadata).
3) Modification anomaly: Inconsistent updates across duplicate rows when an attribute changes in one tuple but remains unchanged in others.

Mentor tip

State any two of insertion anomaly, deletion anomaly, or modification anomaly with a clear description.

(b)

4 marks

Method 1: Transaction log replay (Roll-forward recovery):
Restore the most recent periodic full backup image, then apply sequential changes recorded in the transaction redo log up to the moment immediately preceding corruption.
Method 2: Rollback / Backward recovery (Undo logging):
When an active transaction crashes mid-execution, read uncommitted states from the transaction undo log and reverse all partial writes, returning the database to a consistent checkpoint.

Mentor tip

Describe two distinct mechanisms: roll-forward from backup logs and transaction rollback/undo.

(c)

3 marks

Identify three key duties performed by a Database Administrator (DBA):
1) Database schema design, maintenance, and performance tuning (e.g. creating indexes, managing storage, query optimization).
2) Security and user permission management (configuring user accounts, password policies, access rights, and authentication).
3) Disaster recovery management (scheduling routine backups, verifying backup integrity, executing restoration drills).

Mentor tip

Pick three clear administrative responsibilities: performance/indexing, access rights/security, and backup/recovery.

(d)

3 marks

Describe data masking / pseudonymisation techniques:
1) The DBA can replace real credit card numbers and personal identifiers with synthetic tokens or hash values in operational tables.
2) Dynamic data masking hides all but the final four digits of payment cards (e.g. 'XXXX-XXXX-XXXX-1234') when queried by general staff.
3) Sensitive cardholder tables are encrypted at rest with decryption keys restricted from non-essential third-party services.

Mentor tip

Focus on pseudonymisation, data masking (tokenisation), or column-level encryption with restricted views.

Question 3

19 marks

Music department database normalisation to 3NF and data integrity

Databases

(a)

3 marks

Explain one major benefit of database normalisation:
1) Elimination of redundant data: Each piece of factual information is stored in exactly one logical location.
2) Prevention of update anomalies: Updating an entity's attribute (such as a school's contact number) requires changing only a single row in the parent table.
3) Storage optimization and referential integrity: Tables occupy less disk space and maintain consistency through relational foreign keys.

Mentor tip

Focus on removing redundancy and eliminating the risk of data inconsistency during updates.

(b)

3 marks

Identify three validation or integrity rules for the School_phone_no attribute:
1) Length check: Restrict the field to exactly 9 characters (or standard international phone length).
2) Format / Pattern check: Enforce an input mask permitting only digits and valid separators (e.g. regex `^[0-9]{9}$`).
3) Type / Character check: Disallow alphabetic and special characters, ensuring every input character is numeric.

Mentor tip

Specify concrete validation checks: length check, type check (digits only), and format check (input mask).

(c)

2 marks

Requirements to achieve 1st Normal Form (1NF):
1) Ensure all attributes hold atomic (indivisible) values: multi-valued entries such as `Student_Choice` (e.g. 'VIOLIN, PERCUSSION') and `School_phone_no` must be split so each cell holds a single value.
2) Establish a primary key that uniquely identifies each row without repeating groups.

Mentor tip

Atomicity is the essential keyword: eliminate repeating groups and multi-valued composite cells.

(d)

8 marks

Decompose the unnormalised structure through 1NF, 2NF, and 3NF:
1) STUDENT Table:
STUDENT (Student_ID [PK], First_Name, Family_Name, Date_of_Birth, School_ID [FK])
2) SCHOOL Table (eliminating transitive dependencies on School_Post_Code and School):
SCHOOL (School_ID [PK], School_Name, School_Post_Code)
3) SCHOOL_PHONE Table (handling multiple telephone numbers per school):
SCHOOL_PHONE (School_ID [PK, FK], Phone_Number [PK])
4) INSTRUMENT Table:
INSTRUMENT (Instrument_ID [PK], Instrument_Name)
5) STUDENT_INSTRUMENT Table (resolving M:N relationship between Students and Instruments):
STUDENT_INSTRUMENT (Student_ID [PK, FK], Instrument_ID [PK, FK])

Mentor tip

Make sure composite keys and foreign keys are explicitly marked to link students, schools, phones, and instruments without redundancy.

(e)

3 marks

Distinguish between 2NF and 3NF:
1) 2nd Normal Form (2NF) requires 1NF plus the removal of partial dependencies: every non-key attribute must depend on the whole primary key, not a proper subset of a composite key.
2) 3rd Normal Form (3NF) requires 2NF plus the removal of transitive dependencies: non-key attributes must depend solely on the primary key and never on another non-key attribute.
3) Summary axiom: 'Every non-key attribute must depend on the key, the whole key, and nothing but the key'.

Mentor tip

Contrast partial functional dependency (2NF) with transitive functional dependency (3NF).

Option B: Modelling and simulation · Option

Questions 4–6 · 45 marks

Question 4

18 marks

Ralph second-hand retail pricing model and spreadsheet testing

Modelling and simulation

(a)

4 marks

Specify suitable data types and ranges for the item attributes:
1) Item Type: String / Enumerated type {'furniture', 'lamp', 'musical instrument'}.
2) Brand Recognition: Integer in the range [1, 3] (1 = low, 2 = medium, 3 = high).
3) Condition: String / Enumerated type {'very good', 'good', 'fair'}.
4) Dimensions / Volume: Real (floating point) number $\geq 0$ dm $^{3}$ .

Mentor tip

State both the programmatic data type (String, Integer, Float) and the allowable discrete range for each variable.

(b)(i)

4 marks

Formulate the business rules determining the purchase decision:
Calculate estimated retail value based on brand multiplier, condition weight, and type.
If Estimated Value > 90 AND Purchase Price <= 0.40 * Estimated Value, purchase the item.
If Estimated Value <= 90 OR repair cost exceeds projected markup margin, decline purchase.

Mentor tip

Express rules clearly using logical conditions linking item value, purchase price, and profitability.

(b)(ii)

2 marks

Identify two items that yield a calculated value above 90:
Item 1: High-brand recognized antique furniture in 'very good' condition (e.g. brand = 3, condition = 'very good').
Item 2: Professional musical instrument with medium/high brand status in 'very good' condition (e.g. a branded violin with brand = 2 or 3).

Mentor tip

Choose combinations with brand >= 2 and condition 'very good' to guarantee a valuation > 90.

(c)

2 marks

Calculate the valuation adjustment for damaged goods:
Apply a percentage penalty deduction to the baseline valuation:
Base value $= 100$ , Damage factor reduction $= 30%$ :
$Adjusted Value = 100 \times (1 - 0.30) = 70$
State the revised selling price reflecting the repair overhead and reduced marketability.

Final Price = Base Value \times (1 - Penalty Rate)

Mentor tip

Show numerical steps clearly: subtract the percentage penalty from the base valuation.

(d)

4 marks

Construct an algorithm or formula to compute final selling price:
1) Determine base price from item lookup table based on category and volume.
2) Multiply by brand recognition factor ( $1.0, 1.25, 1.50$ ).
3) Apply condition coefficient (e.g. $1.0$ for 'very good', $0.75$ for 'good', $0.50$ for 'fair').
4) Add standard repair expenses and required profit margin ( $25%$ markup):
$Selling Price = (Base \times Brand \times Condition + Repair) \times 1.25$

Price = (V_{base} \cdot M_{brand} \cdot C_{cond} + Repair) \times (1 + Markup)

Mentor tip

Present a structured formula accounting for condition, brand multiplier, and business profit margin.

(e)

2 marks

Design two test cases for the model verification:
Test 1 (Boundary / Normal test): Input an item with maximum brand rating (3) and 'very good' condition to confirm pricing scales up correctly.
Test 2 (Erroneous / Extreme test): Input invalid brand values (e.g. brand = 0 or 5) or negative repair costs to verify error trapping and validation handling.

Mentor tip

Select one normal/boundary test and one erroneous/extreme data test.

Question 5

19 marks

Bakery queuing simulation, spatial modelling, and validation

Modelling and simulation

(a)

4 marks

Identify the core system variables in the bakery queuing model:
1) Customer arrival rate $λ$ (modelled using a Poisson distribution).
2) Service duration per customer $μ$ (time required to select, prepare, and pay for bread rolls).
3) Number of active servers / staff members ( $n = 2$ ).
4) Queue capacity and physical waiting area footprint.

Mentor tip

Specify arrival rate, service rate, server count, and shop floor spatial constraints.

(b)

3 marks

Explain why a discrete-event simulation is appropriate:
1) The state of the system changes only at discrete points in time when events occur (e.g. a customer arrives, order preparation finishes, a customer departs).
2) Time jumps between successive event occurrences rather than advancing in infinitesimal continuous increments.
3) This enables tracking queue lengths and idle staff intervals efficiently without wasteful continuous numerical integration.

Mentor tip

Link discrete events (arrival, order completed, departure) to system state transitions.

(c)

3 marks

Explain how customer balking / reneging is incorporated:
1) Define a threshold waiting queue length $L_{m a x}$ based on shop floor space.
2) When an arriving customer observes a queue length $\geq L_{m a x}$ , they leave immediately without joining the queue (balking).
3) Record balked customers as lost sales to assess revenue loss resulting from shop size bottlenecks.

Mentor tip

Explain balking when physical capacity is reached and note its impact on lost revenue.

(d)

3 marks

Explain the role of pseudorandom number generators in stochastic simulation:
1) Real customer arrivals and transaction durations vary unpredictably throughout the day.
2) Pseudorandom generation maps uniform values $U (0, 1)$ to service time probability distributions (e.g. exponential or normal).
3) Repeated simulation runs using different random seeds capture variance and generate realistic confidence intervals for peak waiting times.

Mentor tip

Focus on modelling variability in customer arrival intervals and service times.

(e)

6 marks

Propose a verification and validation strategy for the bakery model:
1) Model Verification (Building the model right):
- Trace simulation logic through structured code walkthroughs.
- Verify that under zero arrival rate queue remains zero, and under deterministic inputs outputs match analytical queuing equations ( $M / M /2$ ).
2) Model Validation (Building the right model):
- Gather empirical baseline data by timing actual customer arrivals and service times over several business days.
- Compare simulation output metrics (mean queue length, average wait time) against observed real-world measurements.
- Perform sensitivity analysis by varying parameters to ensure the model responds realistically.

Mentor tip

Clearly separate verification (internal code and mathematical correctness) from validation (comparison with real-world empirical data).

Question 6

8 marks

Automotive ECU sensor processing, control loop latency, and fail-safe operation

Modelling and simulation

(a)(i)

2 marks

State the role of the ECU feedback loop:
1) Continuously poll input sensors (e.g. wheel speed, engine temperature, oxygen levels) via ADC converters.
2) Compare sensed values against target reference thresholds and output corrective actuation signals (e.g. fuel injection, brake pressure) in real time.

Mentor tip

Describe the closed-loop cycle: sense input, compare with setpoint, trigger actuators.

(a)(ii)

2 marks

Explain the consequence of processing latency in vehicle control:
1) Delays in processing sensor readings result in delayed actuator responses (e.g. anti-lock braking modulation).
2) In safety-critical situations at high vehicle speeds, excessive latency can cause control instability, wheel lockup, or increased braking distance.

Mentor tip

Connect latency directly to vehicle instability or prolonged stopping distance during sudden braking.

(b)

4 marks

Describe a fail-safe mechanism in an automotive electronic control unit:
1) Sensor validation check: The ECU monitors sensor health using out-of-range checks and redundant cross-sensor voting.
2) Fail-safe transition: If a sensor produces aberrant or disconnected signals, the system flags a diagnostic trouble code (DTC) and transitions to a degraded 'limp-home' mode.
3) Actuator default: Safety actuators fall back to a mechanical default (e.g. passive hydraulic braking) to maintain driver control without catastrophic failure.

Mentor tip

Explain fault detection, entering a limp-home mode, and defaulting to a safe mechanical state.

Option C: Web science · Option

Questions 7–9 · 45 marks

Question 7

14 marks

Online banking web architecture, browser compatibility, and HTTPS security

Web science

(a)

2 marks

Distinguish between the Internet and the World Wide Web:
1) The Internet is the global hardware infrastructure of interconnected computer networks, routers, and transmission media operating over the TCP/IP suite.
2) The World Wide Web (WWW) is an information-sharing service built on top of the Internet, utilizing HTTP/HTTPS protocols to retrieve and render interlinked hypertext documents.

Mentor tip

Characterize the Internet as the physical network infrastructure and the Web as an application service running on it.

(b)

4 marks

Explain how web standards enable cross-browser compatibility:
1) Web standards defined by the W3C (HTML5, CSS, ECMAScript) provide universal specifications for markup rendering and script execution.
2) All compliant browsers parse standardized HTML/CSS DOM trees and execute JavaScript consistently regardless of underlying vendor engine (Blink, Gecko, WebKit).
3) Server-side banking applications deliver standard RESTful data payloads and standard markup, preventing proprietary client-side incompatibilities.

Mentor tip

Emphasize W3C open standards compliance for HTML, CSS, and ECMAScript across different browser engines.

(c)

2 marks

State two security benefits of HTTPS over HTTP:
1) End-to-end encryption: All request headers, cookies, and transaction payloads are encrypted using TLS/SSL, preventing eavesdropping and packet sniffing.
2) Server authentication and data integrity: Digital certificates issued by trusted Certificate Authorities verify server identity and guarantee that banking data is not altered in transit.

Mentor tip

Highlight encryption (confidentiality) and digital certificates (authentication/integrity).

(d)

3 marks

Explain the function of digital certificates in online banking sessions:
1) The bank's web server presents an X.509 digital certificate containing its public key signed by a reputable Certificate Authority (CA).
2) The user's browser verifies the CA signature against its pre-installed root trust store to confirm the domain belongs to the genuine bank.
3) The client encrypts a symmetric session key using the bank's public key during the TLS handshake, establishing a secure shared secret.

Mentor tip

Explain the role of the Certificate Authority, public key exchange, and preventing man-in-the-middle impersonation.

(e)

3 marks

Explain why client-side scripts alone are insufficient for banking security:
1) Client-side scripts execute in an untrusted environment where tech-savvy users can inspect, bypass, or alter JavaScript validation using browser developer tools.
2) Malicious actors can forge HTTP POST requests directly to banking endpoints without running client scripts.
3) Robust security requires authoritative server-side validation, session authentication, and parameterized query execution for every incoming transaction.

Mentor tip

Emphasize that client-side code can be modified or completely bypassed by an attacker; server validation is mandatory.

Question 8

15 marks

Sports knowledge platform, caching mechanisms, and web search indexing

Web science

(a)

3 marks

Explain how web proxy caching improves website performance:
1) A caching proxy stores copies of frequently requested static assets (images, CSS, media articles) closer to end users.
2) Subsequent client requests for cached assets are served locally by the proxy without traversing the wide area network back to the origin server.
3) This dramatically reduces page load latency, conserves bandwidth, and offloads processing stress from the primary web server.

Mentor tip

Connect local storage of resources to reduced latency and origin server workload relief.

(b)(i)

1 mark

Identify the purpose of a web crawler (spider):
An automated script that systematically traverses hyperlinks across the web to discover and download web pages for search engine indexing.

Mentor tip

State clearly that crawlers traverse hyperlinks to discover and retrieve web pages for index creation.

(b)(ii)

3 marks

Describe how an inverted index organizes sports knowledge documents:
1) During indexing, text is tokenized into distinct keyword stems (e.g. 'marathon', 'hydration').
2) The inverted index maps each unique word to a posting list containing document IDs and term occurrence frequencies.
3) When a user searches for multiple terms, the engine performs fast set intersections across posting lists instead of scanning raw document texts.

Mentor tip

Explain the mapping from keywords/terms to lists of document identifiers where they appear.

(c)

4 marks

Explain how PageRank evaluates page importance:
1) PageRank treats an inbound hyperlink from Page A to Page B as a vote of confidence in Page B's quality.
2) A link from a page with high authority (high PageRank) contributes significantly more weight than a link from an obscure page.
3) The authority passed by a page is divided by its total number of outbound links, preventing link-spam dilution.
4) A damping factor $d \approx 0.85$ models the probability of a user continuing to follow links rather than navigating elsewhere.

P R (u) = \frac{1 - d}{N} + d v \in B_{u} \sum \frac{P R ( v )}{L ( v )}

Mentor tip

Highlight inbound link count, incoming page authority, outbound link division, and the damping factor.

(d)

4 marks

Explain two search engine optimization (SEO) techniques for RunAndBeyond:
Technique 1 (Semantic metadata and structured markup): Incorporate meaningful `<title>`, `<meta description>`, and Schema.org semantic tags so search bots accurately classify sports guides.
Technique 2 (High-quality content and authoritative backlink building): Produce verified, in-depth athletic training literature that encourages organic external citations from sports federations and universities.

Mentor tip

Provide two clear SEO practices: on-page structured metadata and off-page backlink cultivation.

Question 9

16 marks

Mobile web application architecture, offline storage, and cloud synchronization

Web science

(a)(i)

3 marks

Outline how a progressive web application (PWA) operates on mobile devices:
1) The application is developed with standard responsive web technologies (HTML5, CSS, JS) that adapt dynamically to any screen form factor.
2) Service workers run as background threads, intercepting network requests to serve cached assets when offline.
3) A web app manifest enables users to install the web app directly onto their home screen with an app icon without downloading from an app store.

Mentor tip

Mention service workers, responsive layouts, and home screen installation via manifest.

(a)(ii)

2 marks

State two advantages of mobile web apps compared to native mobile applications:
1) Cross-platform code maintainability: A single responsive codebase runs across Android, iOS, and desktop browsers, reducing engineering costs.
2) Instant deployment: Updates published to the web server become immediately accessible to all users without requiring app store approval cycles.

Mentor tip

Focus on cross-platform portability from a single codebase and bypassing app store submission delays.

(b)(i)

2 marks

Identify two local client-side storage mechanisms:
1) IndexedDB: A client-side transactional object-oriented database capable of holding large structured data collections.
2) Web Storage API (localStorage): Key-value string storage suitable for lightweight session preferences and user profiles.

Mentor tip

Name IndexedDB and localStorage (or Cache API) with their roles.

(b)(ii)

5 marks

Describe the synchronization protocol between mobile client storage and central cloud database:
1) Offline data queuing: User actions completed while offline are written locally with universal unique identifiers (UUIDs) and generation timestamps.
2) Connection detection: A network event listener detects the restoration of Internet connectivity.
3) Batch transmission: The client issues HTTPS background POST requests sending the queued transactions to the cloud REST API.
4) Conflict resolution: The server checks timestamps and record version vectors; in case of concurrent edits, it applies a designated resolution policy (e.g. latest timestamp wins or 3-way merge).
5) Acknowledgement and state update: The server confirms successful persistence, prompting the local client to purge the sync queue.

Mentor tip

Walk through the sequence: local queuing, reconnection detection, batch sync, conflict handling (timestamps), and queue clearance.

(c)

4 marks

Evaluate copyright and ethical challenges of content scraping on the web:
1) Intellectual property infringement: Automated scraping reproduces proprietary sports journalism and training datasets without licensing or attribution, depriving creators of ad revenue.
2) Server resource abuse: Aggressive crawlers can flood independent web servers with excessive concurrent requests, degrading performance for human visitors (denial of service).
3) Fair use and terms of service: Web platforms often explicitly prohibit unauthorized extraction in their robots.txt and terms of use, creating legal liabilities for data aggregators.

Mentor tip

Balance intellectual property/revenue loss against technical server load and terms-of-service violations.

Option D: Object-oriented programming · Option

Questions 10–12 · 45 marks

Question 10

13 marks

Hotel loyalty scheme Points class modifiers, constructor overloading, and status query

Object-oriented programming

(a)

4 marks

Outline how access modifiers affect variable access using two non-private examples:
1) `public`: The variable or method is accessible from any other class within the entire application, enabling open access but removing encapsulation.
2) `protected`: The variable is accessible within its own package and by subclasses inheriting from it, supporting extensible class hierarchies while preventing external exposure.
3) Package-private (default): The variable is accessible only to classes residing within the same package.

Mentor tip

Explain public and protected (or package-private), highlighting the difference in scope and inheritance accessibility.

(b)

4 marks

Explain constructor overloading in the Points class:
1) The OOP feature is constructor overloading (a form of compile-time / static polymorphism).
2) Both constructors share the exact same identifier (`Points`) but possess distinct parameter signatures: `Points(String id)` vs `Points(String id, int bp)`.
3) At instantiation, the compiler determines which constructor to execute by evaluating the number and types of arguments provided in the `new` expression.

Mentor tip

Name constructor overloading and explain how distinct parameter lists allow the compiler to bind the appropriate constructor.

(c)

1 mark

Calculate Tim's total points and determine his 2019 status:
Bonus points allocated $= 1000$ .
Total stay duration $= 2 + 1 + 6 = 9 days$ .
Stay points $= 9 \times 1000 = 9000 points$ .
Total points accumulated $= 1000 + 9000 = 10000 points$ .
Status rule: Silver threshold is 10,000 or more but less than 50,000 points.
Tim is assigned: Silver

Total = 1000 + (2 + 1 + 6) \times 1000 = 10000 ⟹ Silver

Mentor tip

Show total calculation: 1000 bonus + 9000 stay points = 10000 points, which meets the 10,000 Silver threshold.

(d)

1 mark

State how an individual object is accessed in the array:
By referencing the array identifier followed by the zero-based integer index enclosed in square brackets, e.g. `allPoints[i]`.

Mentor tip

State that access is achieved using the array index in square brackets.

(e)

3 marks

Construct the `isGold()` method in Java:
```java
public boolean isGold()
{
return statusNow.equalsIgnoreCase("Gold");
}
```
Explanation: The method checks whether the current member's status string equals 'Gold' and returns a boolean flag.

Mentor tip

Use a boolean return type and compare statusNow to 'Gold' using .equals() or .equalsIgnoreCase().

Question 11

25 marks

Hotel Visits class UML, trace output, and points calculation algorithms

Object-oriented programming

(a)

3 marks

Construct the UML diagram for the Visits class:
+------------------------------------------+
| Visits |
+------------------------------------------+
| - hotelCode : String |
| - days : int |
+------------------------------------------+
| + Visits(h : String, d : int) |
| + getDays() : int |
+------------------------------------------+
Key conventions: '-' indicates private attributes, '+' indicates public methods, and types follow colons.

Mentor tip

Draw three distinct boxes with class name, private attributes (-), and public methods (+) with parameter types.

(b)(i)

1 mark

Trace `allPoints[2].getMemberId()`:
`allPoints[2]` was instantiated as `new Points("m102", 2000)`.
Output: m102

Mentor tip

Output is simply the string literal 'm102'.

(b)(ii)

1 mark

Trace `allPoints[0].getBonusPoints()`:
`allPoints[0]` was instantiated using `new Points("m100")` (single argument constructor), which sets `bonusPoints = 0`.
Output: 0

Mentor tip

The 1-arg constructor initializes bonusPoints to 0.

(b)(iii)

1 mark

Trace `allPoints[1].getAllVisits(1).getDays()`:
`allPoints[1]` added `v1` (3 days) at index 0, and `new Visits("h004", 6)` at index 1.
Output: 6

Mentor tip

Visit at index 1 for allPoints[1] has days = 6.

(c)

5 marks

Construct `calculateTotalPoints()` in the Points class:
```java
public int calculateTotalPoints()
{
int totalStayDays = 0;
for (int i = 0; i < y; i++)
{
totalStayDays += allVisits[i].getDays();
}
totalPoints = bonusPoints + (totalStayDays * 1000);
return totalPoints;
}
```
Algorithm: Loop from 0 up to the visit count `y`, accumulate days from each visit via `getDays()`, multiply by 1000, add bonus points, and return the sum.

Mentor tip

Iterate strictly up to y (the number of visits logged) rather than allVisits.length to prevent NullPointerException.

(d)

7 marks

Construct `daysMissing()` in the Points class:
```java
public int daysMissing()
{
int currentEarned = calculateTotalPoints();
int requiredPoints = 0;
if (statusNow.equalsIgnoreCase("Gold"))
{
requiredPoints = 50000;
}
else if (statusNow.equalsIgnoreCase("Silver"))
{
requiredPoints = 10000;
}
else
{
return 0; // Bronze has no minimum point requirement
}
int deficit = requiredPoints - currentEarned;
if (deficit <= 0)
{
return 0;
}
int days = deficit / 1000;
if (deficit % 1000 != 0)
{
days++;
}
return days;
}
```
Explanation: Determine threshold for maintaining statusNow (50,000 for Gold, 10,000 for Silver, 0 for Bronze). Calculate remaining deficit and convert points into integer days needed.

Mentor tip

Handle Bronze as requiring 0 extra days, and ensure that if currentEarned exceeds requiredPoints the method returns 0.

(e)

4 marks

Suggest how the hotel chain can leverage inheritance:
1) Define an abstract superclass `Status` (or `Member`) containing common attributes (memberId, totalPoints, discountRate) and shared methods.
2) Subclasses `GoldMember`, `SilverMember`, and `BronzeMember` inherit from `Status`.
3) Subclasses can override methods such as `applyPerks()` or `calculateBonus()` to provide tier-specific services (e.g. complimentary room upgrades for Gold, late checkout for Silver) without duplicating shared member management code.

Mentor tip

Propose a superclass with common behavior and specialized subclasses overriding benefit methods.

(f)

3 marks

Identify three changes required at annual reset (midnight 31 December):
1) Update member status: Assign `statusNow = statusNextYear;` for all existing members.
2) Reset annual counters: Reset `totalPoints = 0;` and reset the visit counter `y = 0;` for the new operating year.
3) Clear bonus points and visit arrays: Reset `bonusPoints = 0;` (as bonus points apply for the joining year only) and re-instantiate `allVisits = new Visits[366];`.

Mentor tip

Name the three rollover steps: shift statusNextYear into statusNow, reset visit counter y and totalPoints, and clear single-year bonus points.

Question 12

7 marks

Hotel visit analysis algorithm across parallel customer stay history

Object-oriented programming

7 marks

Outline the algorithmic steps to find the hotel with the most customer days:
Step 1: Retrieve the customer's `Points` object from `allPoints` using their `memberId`.
Step 2: Maintain two parallel arrays (or a Hash Map / frequency table) `hotelCodes[]` and `totalDays[]` to track aggregated stay durations per hotel.
Step 3: Loop through all visits of the customer from `0` to `y - 1` using `getAllVisits(i)`.
Step 4: For each visit, extract `hotelCode` and `days`. Search `hotelCodes[]`:
- If `hotelCode` exists, add `days` to the matching index in `totalDays[]`.
- Otherwise, append `hotelCode` to `hotelCodes[]` and set `totalDays` to `days`.
Step 5: Perform a linear scan over `totalDays[]` to identify the maximum day count and note the corresponding `hotelCode`.
Step 6: Query the `Hotel` collection to find the `Hotel` object whose ID matches the identified `hotelCode` and retrieve its name attribute.
Step 7: Output or return the resulting hotel name.

Mentor tip

Clearly describe aggregating days per unique hotelCode across all customer visits, locating the maximum total, and looking up the hotel name.

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
Inadvertent inclusion of non-matching loan amounts · Q1
The SQL query requires Amount > 600000. An amount of exactly 500000 or lower must be excluded even if the type matches Home.
02
Confusing 2NF partial dependencies with 3NF transitive dependencies · Q3
2NF eliminates functional dependencies on a part of a composite primary key, whereas 3NF eliminates functional dependencies between non-key attributes.
03
Looping past active visits in array · Q11
The allVisits array has length 366, but only y elements contain instantiated Visit objects. Iterating to allVisits.length causes a NullPointerException.

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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