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computer science > 3. data representation > Flashcards

3. data representation Flashcards

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1
Q

natural number

A

is a whole number used in counting

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2
Q

rational number

A

any value that can be expressed as a ratio, or fraction. this includes integer values since each can be simply expressed as 7/1 or 1076/1.

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3
Q

irrational number

A

such as pi cannot be expressed as a fraction and which has an endless series of non-repeating digits.

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4
Q

ordinal numbers

A

natural numbers used to describe the numerical position or order of objects: first in race, second turn on the left.
they are used as pointers to a particular element in a sequence, or to define the position of something in a list, for example an array pointer.
characters and integers are examples of ordinal data types.

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5
Q

number bases

A

binary - a number system that only use digits 1s and 0s and has a base 2.

denary - a number system that uses the digits 0 through 9 and has a base 10.

hexadecimal - a system that uses digits 0-9 and letters A to F and has a base of 16.

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6
Q

why is the hexadecimal number system used?

A
  • its easier for humans to understand and write
  • fewer mistakes are likely to be made in writing
  • simple to represent a byte in just two digits
  • easier to remember than a 24-bit binary string (as colour codes in images often use hexadecimal to represent the RGB values)
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7
Q

byte

A

8 bits

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8
Q

bit

A

a binary digit used by computers as the fundamental unit of information

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9
Q

signed binary

A

a binary number system that can represent both positive and negative numbers

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10
Q

unsigned binary

A

a binary number system that can only represent positive numbers

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11
Q

ASCII (american standard code for information interchange)

A

a character set used to represent alphanumeric characters or symbols as set of 7 bits.

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12
Q

ASCII information

A

1st 32 codes represent non-printing characters used for control such as backspace (code 8), enter or carriage return key (code 13) and the escape key (code 27).
space character is also included as code 32 and delete as 127

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13
Q

unicode

A
  • a character set that is a superset of ASCII. its used to represent alphanumeric characters or symbols as an integer code point which is equal tot he characters ASCII code
  • 8 bit version was developed to include an additional 128 combinations to represent symbols (page 74 tb)
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14
Q

unicode information

A

encodings take more storage space than ASCII, significantly increasing the file sizes and transmission times.

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15
Q

parity bits

A

a method of checking binary codes for errors during data transmission by counting the numbers 1s and 0s present

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16
Q

majority voting

A

a method of checking binary codes for errors during data transmission by sending each bit multiple times

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17
Q

check digits

A

a method of checking codes for errors during data transmission by adding an extra digit to the end (usually calculated/processed from digits in the code itself) that checks whether the data is accurate

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18
Q

checksum

A

is a mathematical algorithm that us applied to a ‘unit’ or packet of data

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19
Q

fixed point form

A

a form used to represent numbers with a fractional part in any number system.

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20
Q

fixed point binary numbers

A

useful way to represent fractions in binary

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21
Q

binary point

A

is used to separate the whole place values from the fractional part on a number line

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22
Q

twos complement

A

a coding scheme used in signed binary to represent negative as well as positive numbers. a negative number is represented by flipping all its digits and adding 1 to the most significant bit.

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23
Q

character code

A

a unique binary representation of a character. not to be confused with the binary representation of a decimal digit, which is its numerical value in the binary system.

24
Q

resolution

A

a measure of the total number of pixels in an image, typically expressed in terms of the number of pixels per inch.
the resolution of an image can be expressed as the width in pixel x height in pixels.

the greater the number of pixels, the sharper the image as the the pixels must become smaller to fit inside its boundaries

25
Q

PPI

A

pixels per inch
indicates the density of the pixels rather than the actual image dimensions

26
Q

colour depth

A

a measure of the amount of colour used in an image, expressed in terms of the number of bits per pixel

27
Q

metadata

A

data about data. in the case of image metadata, details/properties of an image include, width, height and colour depth

28
Q

vector images

A

made up of geometric shapes or objects such as lines, curves arcs and polygons

29
Q

vector file

A

stores only the necessary details about each shape in order to redraw the object when the file loads

30
Q

drawing list

A

specifies how to redraw the image

31
Q

state one advantage of vector graphics compared with bitmapped graphics

A
  • use less memory and storage space
  • transmit faster
  • often load more quickly
  • has much smaller file size
  • scale perfectly, regardless how large or small you make it
32
Q

to represent sound in a computer

A

the (continuous) analogue sound waves had to be converted to a (discrete) digital format. this can be done by measuring and recording the amplitude of sound wave at given time intervals. the more frequent the samples are taken, the more accurately the sound will be represented

33
Q

frequency

A

measured in hertz, a unit of frequency equal to one cycle per second

34
Q

sampling rate

A

the number of samples taken per second

35
Q

sample resolution

A

the number of bits used to represent a single sample

36
Q

sound sampling

A

the process of converting analogue sound waves to a digital waveform, by storing a finite number of readings in binary

37
Q

calculating sound sample sizes

A

the number of samples per second x the number of bits per minute x the length of the sample in seconds

38
Q

analogue to digital conversion

A

a microphone converts the sound energy into electrical energy. ADC samples the analogue data at a given frequency, measuring the amplitude of the wave at each point and converting it into a binary value according to the resolution or audio bit depth being used for each sample. to output sound, the binary values for each sample point are translated back into analogue signals and sent to an amplifiers connected to a speaker

39
Q

DAC

A

converting a digital audio signal to an analogue signal

40
Q

frequency of sound

A

is determined by the speed of oscillation or vibration of a wave. this controls the pitch and is measured in hertz

41
Q

Nyquist theorem

A

1928 discovered in order to produce an accurate recording, the sample rate must be at least double that of the highest frequency in the original signal. his theory was later proven by clause shannon in 1949

42
Q

MIDI

A

is a technical standard that describes a protocol, digital interface and connectors which can be used to allow a wide variety of electronic musical instruments, computers and other related devices to connect and communicate with one another

“MIDI is a protocol for ADC audio transmission to a digital interface used for the majority of electronic musical instruments and computers”

43
Q

midi controller

A

carries event messages that specify pitch and duration of a note, timbre, vibrato and volume changes, and synchronize tempo between multiple devices.

44
Q

why use compression?

A

file compression techniques were developed to reduce the storage space of files on disk

45
Q

lossy compression

A

unnecessary information is removed from the original permanently
e.g. JPG - show artefacts as consequence, MP3 file to remove frequencies to high for most of us to hear and remove quieter sounds that are played at the same time as louder sounds

46
Q

how does lossless compression work?

A

by recording patterns in data rather than the actual data. using these patterns and a set of instructions on how to use them, the computer can reverse the procedure and reassemble an image, sound or text file with exact accuracy and no data is lost.

47
Q

lossless compression

A

retains all information required to replicate the original file exactly

48
Q

run-length encoding

A

a type of lossless compression where repeated occurrences of the same data (like several pixels of the same colour in an image) are stored as single data values with their counts
“records its value and number of times it repeats”

49
Q

dictionary based coding

A

a type of lossless compression algorithm searches through the text to find suitable entries in its own dictionary and translates the message accordingly

50
Q

encryption

A

is the transformation of data from one form to another to prevent an unauthorised third party from being able to understand.
the original data is known as plaintext.
the encrypted data is known as ciphertext

51
Q

the encryption method/algorithm

A

is known as cipher

52
Q

key

A

secret information to lock or unlock the message is known as the a key

53
Q

caesar cipher

A

also known as shift cipher is a type of substitution cypher that works by shifting the letters of the alphabet along by a given number of characters; this parameter being the key.
(A is parallel/opposing to F at the beginning of the alphabet)

54
Q

vernam cipher

A

a cipher that uses a one-time pad (a secret random key) to convert each character to cipher text by modularly adding it with corresponding character of the key.
this is impossible to decrypt without key

55
Q

one-time pad

A

to provide perfect security, the encryption key or one-time pad must be equal to or longer in characters than plain text, be truly random and only used once.
the sender and recipient must meet in person to securely share the key and destroy it after encryption or decryption. since the key is random, so will be the distribution of the characters meaning that no amount of cryptanalysis will produce meaningful results.

computer science (12 decks)

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