PAPER 2 - COMPUTER SCIENCE OCR - J277 QUESTIONS AND CORRECT ANSWERS

PAPER 2 - COMPUTER SCIENCE OCR
- J277 QUESTIONS AND CORRECT
ANSWERS



Abstraction - ans- ws ws


Hiding or removing irrelevant details from a problem to reduce complexity.
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Decomposition - ans-Breaking a complex problem down into smaller problems.
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Input sanitization - ans-Cleaning up data entered by removing non-
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standard characters. ws




Casting - ans- ws ws


Converting one data type to another, for example converting an integer to a real nu
ws ws ws ws ws ws ws ws ws ws ws ws ws ws


mber.

Sequence - ans-the order in which the program is written and executed.
ws ws ws ws ws ws ws ws ws ws ws




Variable - ans-A location for a memory
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Arrays - ans-allows multiple items of data to be stored under one identifying name
ws ws ws ws ws ws ws ws ws ws ws ws ws




SQL - ans-ws ws


SELECT (the fieldname of the data to be selected), FROM ( the name of the databa
ws ws ws ws ws ws ws ws ws ws ws ws ws ws ws


se table), WHERE (condition in a fieldname is met)
ws ws ws ws ws ws ws ws




High Level Language: - ans-- Uses English-like words
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- Must be translated before the processor can execute
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- Code is portable between different processors
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- Human oriented code written by programmers
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- One high level command equates to many machine code instructions
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Describe the advantages of writing the program in a high-
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level language instead of in assembly language (2) - ans-- Easier/
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quicker for humans to write
ws ws ws ws


- Easier/quicker to read / understand / remember
ws ws ws ws ws ws ws


- Easier/quicker to maintain / debug / spot errors
ws ws ws ws ws ws ws ws


- ...because code is closer to English / uses English words
ws ws ws ws ws ws ws ws ws ws

, - Less code to write
ws ws ws ws


- ...because one HLL instruction represents many assembly instructions
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- Portable (between processors) // will work with different types of computer
ws ws ws ws ws ws ws ws ws ws ws




Describe how a character set is used to represent the string value stored in the vari
ws ws ws ws ws ws ws ws ws ws ws ws ws ws ws


able name (2) - ans--
ws ws ws ws


Each character (in character set) has a unique (binary) number/value
ws ws ws ws ws ws ws ws ws ws


- Each character in the string is assigned its associated number/value
ws ws ws ws ws ws ws ws ws ws


- The (binary) value of each character is stored/combined (in order)
ws ws ws ws ws ws ws ws ws ws


- ... by example e.g. The binary value for D, then for r, then for u
ws ws ws ws ws ws ws ws ws ws ws ws ws ws ws


Uses ASCII/Extended ASCII/Unicode
ws ws




The vending machine is tested before it is released. (i) Explain the purpose of testin
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g the vending machine. (2) - ans-- Check the program meets the user requirements
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- Check the program works (as intended) // detect logic / syntax errors
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- Check the program does not crash (under invalid entry) //
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check error messages are suitable
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- ...allow these errors to be fixed
ws ws ws ws ws ws


- ...make sure there are no problems when released
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- Any suitable example related to the vending machine e.g. gives correct change
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CANNOT ACCEPT 'FIND ERRORS/ BUGS' OR 'FIXES ERRORS'
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Describe the difference between iterative testing and final testing (2) - ans--
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Iterative is during development // repeatedly testing after/while making changes
ws ws ws ws ws ws ws ws ws ws


- Final is when the development is (almost) complete // done after iterative testing
ws ws ws ws ws ws ws ws ws ws ws ws ws




Ways that the maintainability of the program can be improved. - ans-- Indentation //
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whitespace
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- Appropriately named variables / identifiers
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- Modularization / use of subroutines
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- Comments
ws


- Use of constants
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Give two reasons why computer scientists use hexadecimal to represent numbers in
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stead of binary. (2) - ans-- Easier/quicker to communicate / enter / write / read /
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remember
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- Less chance of input errors // easier to spot errors
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- They are smaller / shorter
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- Easy to convert between binary and Hexadecimal
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State what is meant by the term image resolution (1) - ans--
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Number of pixels (in an image)
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- Height and width (of an image)
ws ws ws ws ws ws




Give two ways that the file size of the image could be reduced. - ans--
ws ws ws ws ws ws ws ws ws ws ws ws ws ws


Reduce number of pixels / resolution
ws ws ws ws ws ws