2023 Cambridge IAS-Level Computer Science (9618) 模擬試題連答案詳解

Explain the purpose and function of a device driver in a computer system.

Describe how Carrier Sense Multiple Access with Collision Detection (CSMA/CD) handles a collision on a shared network medium.

Explain what is meant by the term 'sampling resolution' in relation to the digital representation of sound.

Explain the concept of 'referential integrity' in a relational database and how it is enforced.

An analyst is designing a database for a medical clinic. They are reviewing several tables to ensure they are normalized correctly.

Match each of the following database scenarios (A to D) with the correct database concept or normalization state from the list:
- 1NF (First Normal Form)
- 2NF (Second Normal Form)
- 3NF (Third Normal Form)
- Partial Dependency
- Transitive Dependency
- Referential Integrity

Scenarios:
- Scenario A: A table PatientPrescription has a composite primary key (PatientID, DrugID). The attribute PatientName depends only on PatientID. What is this relationship called?
- Scenario B: A table has a single primary key AppointmentID. There are no non-key fields that depend on other non-key fields. Every attribute contains only atomic values. What is the highest normalization state this table is guaranteed to be in?
- Scenario C: A developer ensures that every value in the DoctorID column of the Appointments table matches an existing DoctorID in the Doctors table. What database principle is being maintained?
- Scenario D: In a table with primary key ClinicID, the attribute ManagerEmail depends on ManagerID, which in turn depends on ClinicID. What is this relationship called?

A database designer is normalizing a database for a book store.
The unnormalised relation is:
BookSales(InvoiceNo, CustomerID, CustomerName, CustomerAddress, (BookID, Title, Author, Qty, Price))
Where (BookID, Title, Author, Qty, Price) represents a repeating group.

Identify the correct database term, attribute, or relational schema for each of the following database design steps:
1. Identify the composite primary key of the new transaction details table required to transition this relation to 1NF.
2. To move to 2NF, we must separate customer details into a new table. State this table's schema in standard notation: TableName(PrimaryKey, Attribute1, ...), indicating the primary key clearly.
3. Identify the database term for the relationship where Author is dependent only on BookID in a table with composite key (InvoiceNo, BookID).
4. If a separate 2NF table Book(BookID, Title, PublisherID, PublisherAddress) is kept, where PublisherAddress is functionally dependent on PublisherID, state which normalization form is violated.

An engineering firm uses a database to track projects, employees, and their roles. The following schema is in 1NF:
ProjectAllocation(ProjectID, EmployeeID, ProjectName, ProjectBudget, EmployeeName, Role, HourlyRate)
The primary key is the composite key: (ProjectID, EmployeeID).

Match each database design task or observation (1 to 4) to its correct database term, normalization form, or schema definition:
1. In ProjectAllocation, ProjectName and ProjectBudget depend only on ProjectID, which is part of the composite key. State the database term for this relationship.
2. Write the 2NF relation schema (including its primary key) that should be created to hold project details in standard notation.
3. In a 2NF relation Allocation(ProjectID, EmployeeID, Role, HourlyRate), the HourlyRate is functionally determined by the Role (where Role is a non-key attribute). State the database term for this dependency between (ProjectID, EmployeeID) and HourlyRate.
4. State the normalization level of the following set of tables:
- Project(ProjectID, ProjectName, ProjectBudget)
- Employee(EmployeeID, EmployeeName)
- Allocation(ProjectID, EmployeeID, Role)
- RoleRate(Role, HourlyRate)

Perform the binary addition of the following two 8-bit unsigned binary integers. Show your working and state whether an overflow error has occurred:

01101100
+ 10100101

Convert the denary value \(-43\) into an 8-bit signed binary integer using two's complement representation. Show your working.

Convert the denary number 385 into Binary Coded Decimal (BCD) format.

Convert the hexadecimal number BD into an unsigned denary integer. Show your working.

Perform the addition of the following two 8-bit two's complement binary integers. Show your working and state the final 8-bit result:

11111010
+ 00001101

A logic circuit has three inputs: \(A\), \(B\), and \(C\). The output \(X\) is produced by an OR gate. The inputs to this OR gate are:
- The output of a NAND gate with inputs \(A\) and \(B\).
- The output of an XOR gate with inputs \(B\) and \(C\).

Write the Boolean expression that represents this logic circuit. You may use standard algebraic notation or text-based logical operators.

An electronic control system evaluates the Boolean expression:
\(X = (A \cdot \overline{B}) + \overline{B \cdot C}\)

Determine the logical value (0 or 1) of the output \(X\) for the following two sets of inputs:
1. \(A = 1, B = 1, C = 1\)
2. \(A = 0, B = 1, C = 0\)

Explain the interaction between the Program Counter (PC) and the Memory Address Register (MAR) during the Fetch stage of the Fetch-Execute cycle.

Explain how a network switch directs data packets within a Local Area Network (LAN) and why this makes it more secure and efficient than a network hub.

Explain how an operating system uses paging to manage physical memory, including the role of the page table.

At the end of a Fetch-Execute cycle, the CPU checks for active interrupts. Explain the sequence of steps the CPU performs if an active interrupt is detected.

Explain the role of a router in directing data packets between different networks.

Explain the role of a device driver and why it is necessary for communication between the Operating System (OS) and a hardware device.

An Integrated Development Environment (IDE) provides features to help a programmer debug their code.

Explain how the following two features assist in debugging:
1. Breakpoints
2. Single-stepping

A programmer writes two code segments. For each segment, state the type of error (Syntax, Runtime, or Logic) that occurs and justify your answer.

Segment 1:
`IF Value = 10`
` OUTPUT "Value is ten"`
`ENDIF`
(Note: The syntax rules of the language require the keyword `THEN` after the condition, which is missing.)

Segment 2:
`Average <- Total / Count`
(Note: During execution, the variable `Count` has a value of 0, causing the program to crash with a 'Division by Zero' error.)

An algorithm is designed to process a sequence of positive integers ending with a sentinel value of -1.

The logic is represented by the following flowchart steps:
1. Initialize `Count` to 0, `Sum` to 0.
2. Input the first number into `Num`.
3. Loop while `Num` is not equal to -1:
a. If `Num` is even (i.e., `Num MOD 2 = 0` is true), update `Sum <- Sum + Num`.
b. Otherwise, update `Count <- Count + 1`.
c. Input the next number into `Num`.
4. Output `Sum` and `Count`.

Complete the trace table below for the input sequence: **10, 15, 18, -1**

$$\begin{array}{|c|c|c|c|} \hline \text{Num} & \text{Sum} & \text{Count} & \text{Output} \\hline & 0 & 0 & \\hline & & & \\hline & & & \\hline & & & \\hline & & & \\hline \end{array}$$

A flowchart contains a decision process defined by the following sequential operations:
1. Input `BaseSalary` (a real number representing a monthly salary).
2. If `BaseSalary` is strictly greater than 4000:
- Set `TaxRate` to 0.25
- Set `Bonus` to 300
3. Otherwise:
- Set `TaxRate` to 0.15
- Set `Bonus` to 150
4. Calculate `NetSalary` using the formula: \( NetSalary = BaseSalary - (BaseSalary \times TaxRate) + Bonus \)
5. Output `NetSalary`.

Write 9618 pseudocode that corresponds to this flowchart logic. You must include appropriate variable declarations.

A programmer is designing a program to store data about video games in a collection. Each game has a unique code GameID (e.g., 'G105'), a name Title (e.g., 'Space Quest'), and a price Price (e.g., 49.99). Write pseudocode to: 1. Define a user-defined record type named Game. 2. Declare a 1D array named Inventory that can store up to 100 Game records, indexed from 1.

An array of records is defined using the following pseudocode:

TYPE Participant
DECLARE Name : STRING
DECLARE Active : BOOLEAN
ENDTYPE

DECLARE Club : ARRAY[1:50] OF Participant

Write the pseudocode statement(s) to:
1. Assign the value TRUE to the Active status of the 25th participant in the Club array.
2. Print the Name of the last participant in the array.

Write a pseudocode function `ExtractScores` that takes a string `CSVLine` containing exactly 5 integer scores separated by semi-colons (for example, `"85;92;78;90;88"`).

The function must parse these scores and store them in a 1D array `ScoreArray` of 5 integers, which is passed by reference.

The function must return `TRUE` if all 5 scores are successfully parsed and each score is in the range 0 to 100 inclusive. It must return `FALSE` if any score is outside this range, or if the string does not contain exactly 5 scores.

You can assume standard string manipulation functions:
- `LENGTH(s : STRING) RETURNS INTEGER`
- `MID(s : STRING, start : INTEGER, length : INTEGER) RETURNS STRING` (index starts at 1)
- `TONUM(s : STRING) RETURNS INTEGER` (converts numeric string to integer)

An array of strings `Queue` contains some elements representing names, and others representing empty slots (indicated by an empty string `""`).

Write a pseudocode procedure `ShiftQueue` that takes two parameters:
- `Queue`: a 1D array of strings (passed by reference)
- `MaxSize`: the integer size of the array

The procedure must shift all non-empty elements to the left to close any empty slots (retaining their relative order), and fill the remaining rightmost elements with `""`.

For example, if `Queue` initially contains:
`["", "Alice", "Bob", "", "Charlie", ""]` and `MaxSize` is 6,
after calling `ShiftQueue`, the array must contain:
`["Alice", "Bob", "Charlie", "", "", ""]`.

A teacher stores student attendance in a 2D array `Attendance` of size 30 rows by 5 columns, representing 30 students and 5 school days. `Attendance[R, C]` is either `TRUE` (present) or `FALSE` (absent).

Write a pseudocode function `PerfectAttendance` that takes:
- `Attendance`: the 2D array of BOOLEAN values (passed by value)
- `PerfectStudents`: a 1D array of 30 integers (passed by reference)

The function must search the `Attendance` array and identify the row index (1 to 30) of any student who was present on all 5 days. These row indices must be stored in the `PerfectStudents` array starting from index 1.

The function must return the total number of students with perfect attendance.

A sequential text file Stock.txt contains stock level information for a retail store. The data for each stock item is stored across three consecutive lines:
- Line 1: Item ID (a string, e.g., "XY1054")
- Line 2: Quantity in stock (an integer)
- Line 3: Unit Price (a real number)

An Item ID must be validated before the stock record is processed. A valid Item ID must meet the following rules:
- It must be exactly 6 characters long.
- The first two characters must be uppercase alphabetic characters ('A' to 'Z').
- The remaining four characters must be digits ('0' to '9').

Write pseudocode for a function CalculateTotalValue which:
- Takes an integer parameter MinStock representing a threshold quantity.
- Reads all records from Stock.txt.
- Validates the Item ID for each record.
- If the Item ID is valid and the Quantity is greater than or equal to MinStock, calculates the total stock value for that item (Quantity multiplied by Unit Price) and adds it to a running total.
- Closes the file and returns the accumulated total value.

A sequential text file Members.txt stores information about members of a sports club. Each member's record is stored on a single line as a fixed-width string of exactly 15 characters, structured as follows:
- Characters 1 to 7: Member ID (e.g., "MBR8904")
- Characters 8 to 11: Birth Year (e.g., "1998")
- Character 12: Membership Level (either 'G' for Gold, 'S' for Silver, or 'B' for Bronze)
- Characters 13 to 15: Status (either "ACT" for Active or "INA" for Inactive)

A member record is considered valid if and only if it meets all the following criteria:
- The Member ID starts with "MBR" followed by exactly four digits ('0' to '9').
- The Birth Year consists only of digits and is between 1940 and 2010 inclusive.
- The Membership Level is one of the characters: 'G', 'S', or 'B'.
- The Status is either "ACT" or "INA".

Write pseudocode for a function CountValidGoldMembers which:
- Takes no parameters.
- Reads all records from Members.txt.
- Validates each record according to the rules above.
- Counts how many valid members have a Membership Level of 'G' (Gold) and a Status of "ACT" (Active).
- Closes the file and returns the total count as an integer.

A software developer is using a top-down integration testing approach to test a program consisting of a main module, ProcessOrder, which calls a lower-level module, CalculateTax. At this stage of development, CalculateTax has not yet been written. Explain how a stub is used to test the ProcessOrder module in this scenario.

A validation function ValidateAge(Age : INTEGER) returns TRUE if the input Age is in the valid range of 18 to 65 inclusive, and FALSE otherwise. State three distinct test cases that would be used to perform Boundary Value Analysis (BVA) specifically around the lower limit of the range. For each test case, state the input value and the expected outcome.

A software company is developing a mobile application where the client's requirements are expected to change frequently throughout the development cycle. Explain three reasons why an Agile software development model is more suitable than a traditional Waterfall model for this project.