9608_s15_qp_32
A paper of Computer Science, 9608
Questions:
6
Year:
2015
Paper:
3
Variant:
2
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1
The following syntax diagrams, for a particular programming language, show the syntax of: • an assignment statement • a variable • a letter • an operator Variable Assignment statement Variable Letter = Variable Operator Variable a b c d ; Letter Letter Letter Operator + – ÷ The following assignment statements are invalid. Give the reason in each case. a = b + c Reason a = b – 2; Reason a = dd * cce; Reason Write the Backus-Naur Form (BNF) for the syntax diagrams shown on the opposite page. ::= ::= ::= ::= Rewrite the BNF rule for a variable so that it can be any number of letters. ::= Programmers working for a software development company use both interpreters and compilers. The programmers prefer to debug their programs using an interpreter. Give one possible reason why. The company sells compiled versions of its programs. Give a reason why this helps to protect the security of the source code.
3. Advanced Theory  →  3.4. System software
2. Fundamental Problem-solving and Programming Skills  →  2.3. Programming
Open
2
The incomplete table below shows descriptions and terms relating to malware. Complete the table with appropriate descriptions and terms. Description Term A Unsolicited emails containing advertising material sent to a distribution list. B A standalone piece of malicious software that can reproduce itself automatically. C Pharming D Phishing For one of the terms, describe: • a problem that might arise for a user • a possible solution to the problem Choose between the terms: A / B (circle your choice) Problem Solution Explain the following terms: Encryption Public key A user downloads software from the Internet. State what should be part of the download to provide proof that the software is authentic. Describe the process for ensuring that the software is both authentic and has not been altered.
3. Advanced Theory  →  3.5. Security
Open
3
A particular programming language allows the programmer to define their own data types. ThisDate is an example of a user-defined structured data type. TYPE ThisDate DECLARE ThisDay : (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31) DECLARE ThisMonth : (Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec) DECLARE ThisYear : INTEGER ENDTYPE A variable of this new type is declared as follows: DECLARE DateOfBirth : ThisDate Name the non-composite data type used in the ThisDay and ThisMonth declarations. Name the data type of ThisDate. The month value of DateOfBirth needs to be assigned to the variable MyMonthOfBirth. Write the required statement. Annual rainfall data from a number of locations are to be processed in a program. The following data are to be stored: • location name • height above sea level (to the nearest metre) • total rainfall for each month of the year (centimetres to 1 decimal place) A user-defined, composite data type is needed. The programmer chooses LocationRainfall as the name of this data type. A variable of this type can be used to store all the data for one particular location. Write the definition for the data type LocationRainfall. The programmer decides to store all the data in a file. Initially, data from 27 locations will be stored. More rainfall locations will be added over time and will never exceed 100. The programmer has to choose between two types of file organisation. The two types are serial and sequential. Give two reasons for choosing serial file organisation.
3. Advanced Theory  →  3.1. Data representation
4. Further Problem-solving and Programming Skills  →  4.1. Computational thinking and problem-solving
Open
4
Complete the truth table for this logic circuit: A B X A B Working space X Complete the truth table for this logic circuit: A B X A B Working space X A student decides to write an equation for X to represent the full behaviour of each logic circuit. Write the Boolean expression that will complete the required equation for X for each circuit: Circuit 1: X = Circuit 2: X = Write the De Morgan’s Law which is shown by your answers to part and part . Write the Boolean algebraic expression corresponding to the following logic circuit: A B X Using De Morgan’s laws and Boolean algebra, simplify your answer to part . Show all your working.
3. Advanced Theory  →  3.3. Hardware
Open
5
A gardener grows vegetables in a greenhouse. For the vegetables to grow well, the temperature needs to always be within a particular range. The gardener is not sure about the actual temperatures in the greenhouse during the growing season. The gardener installs some equipment. This records the temperature every hour during the growing season. Name the type of system described. Identify three items of hardware that would be needed to acquire and record the temperature data. Justify your choice for each. Item 1 Justification Item 2 Justification Item 3 Justification The equipment records temperatures in the greenhouse. It does this for seven locations. Each recording is stored as two successive bytes. The format is shown below: Greenhouse location Temperature reading Byte 1 Byte 2 The location is indicated by the setting of one of the seven bits in byte 1. For example, location 4 is indicated by setting bit 4. Bit 0 of byte 1 acts as a flag: • the initial value is zero • when the reading has been processed it is set to 1 Byte 2 contains the temperature reading (two’s complement integer). Interpret the data in byte 1 shown below: Byte 1 Byte 2 The system receives a temperature reading of –5 degrees from sensor 6. Complete the boxes below to show the two bytes for this recording. The reading has not yet been processed. Byte 1 Byte 2 The accumulator is loaded with the value of byte 1 from location 106. Write the assembly language instruction to check whether the reading in byte 2 came from location 4. LDD 106 // data loaded from address 106 Write the assembly language instruction to set the flag (bit 0) of the byte contained in the accumulator to 1.
3. Advanced Theory  →  3.6. Monitoring and control systems
1. Theory Fundamentals  →  1.4. Processor fundamentals
Open
6
Four descriptions and three protocols are shown below. Draw a line to connect each description to the appropriate protocol. Description Protocol used email client downloads an email from an email server HTTP email is transferred from one email server to another email server POP3 email client sends email to email server SMTP browser sends a request for a web page to a web server Downloading a file can use the client-server model. Alternatively, a file can be downloaded using the BitTorrent protocol. Name the model used. For the BitTorrent protocol, explain the function of each of the following: Tracker Seed Swarm To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge International Examinations Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cie.org.uk after the live examination series.
3. Advanced Theory  →  3.2. Communication and Internet technologies
Open