data - basics

data - basics

difference between data and information

Computers need data. Humans need information.

Data is a building block. Information gives meaning and context.

Example :

20180101 is the raw data. It is a suite of 8 numbers.

Interpreted as a date it is the 1st january 2018.

It could be also a transaction amount of around 20 millions (euros ? dollars ?).

It could be a (bad) password, it could be a lot of things.

To become an information, the data need context.

anglicismes

Beaucoup de confusions terminologiques sont faites en français du fait de mauvaises traductions qui affectent le sens.

digital et numérique

Par exemple digit en anglais signifie chiffre.

Ce qui conduit certaines personnes à parler de digital au lieu de numérique.

L'informatisation du monde est le processus de transformation de l'information en nombres, il s'agit donc de numérisation et non de digital. En français digital se rapporte aux doigts.

chiffrement et cryptage

Il en va de même pour chiffrement et cryptage (anglicisme de encryption).

bit et octet

En anglais bit se traduit bit. Pas de différence.

En revanche octet se traduit byte.

Un octet étant composé de 8 bits, parler de 10 megabits par seconde n'est pas du tout équivalent à 10 megabytes par seconde !

data

bit

The smallest piece of data. Short for binary digit (chiffre binaire).

A bit has a single binary value, either 0 or 1.

byte

A byte is a unit of data that is eight binary digits long.

Example, the number 73 in decimal base is 01001001 in binary base.

data structure

text

The first data structure for text is the ASCII (American Standard Code for Information Interchange)

128 characters available (0 to 127) expressed in a table :

Dec Hexa Oct Html chr binary description
0 0 0 NUL 0000000 (null)
1 1 001 SOH 0000001 (start of heading)
2 2 002 STX 0000010 (start of text)
3 3 003 ETX 0000011 (end of text)
4 4 004 EOT 0000100 (end of transmission)
5 5 005 ENQ 0000101 (enquiry)
6 6 006 ACK 0000110 (acknowledge)
7 7 007 BEL 0000111 (bell)
8 8 010 BS 0001000 (backspace)
9 9 011 TAB 0001001 (horizontal tab)
10 A 012 LF 0001010 (NL line feed, new line)
11 B 013 VT 0001011 (vertical tab)
12 C 014 FF 0001100 (NP form feed, new page)
13 D 015 CR 0001101 (carriage return)
14 E 016 SO 0001110 (shift out)
15 F 017 SI 0001111 (shift in)
16 10 020 DLE 0010000 (data link escape)
17 11 021 DC1 0010001 (device control 1)
18 12 022 DC2 0010010 (device control 2)
19 13 023 DC3 0010011 (device control 3)
20 14 024 DC4 0010100 (device control 4)
21 15 025 NAK 0010101 (negative acknowledge)
22 16 026 SYN 0010110 (synchronous idle)
23 17 027 ETB 0010111 (end of trans. block)
24 18 030 CAN 0011000 (cancel)
25 19 031 EM 0011001 (end of medium)
26 1A 032 SUB 0011010 (substitute)
27 1B 033 ESC 0011011 (escape)
28 1C 034 FS 0011100 (file separator)
29 1D 035 GS 0011101 (group separator)
30 1E 036 RS 0011110 (record separator)
31 1F 037 US 0011111 (unit separator)
32 20 040   Spc 0100000 (space)
33 21 041 ! ! 0100001
34 22 042 " " 0100010
35 23 043 # # 0100011
36 24 044 $ $ 0100100
37 25 045 % % 0100101
38 26 046 & & 0100110
39 27 047 ' ' 0100111
40 28 050 ( ( 0101000
41 29 051 ) ) 0101001
42 2A 052 * * 0101010
43 2B 053 + + 0101011
44 2C 054 , , 0101100
45 2D 055 - - 0101101
46 2E 056 . . 0101110
47 2F 057 / / 0101111
48 30 060 0 0 0110000
49 31 061 1 1 0110001
50 32 062 2 2 0110010
51 33 063 3 3 0110011
52 34 064 4 4 0110100
53 35 065 5 5 0110101
54 36 066 6 6 0110110
55 37 067 7 7 0110111
56 38 070 8 8 0111000
57 39 071 9 9 0111001
58 3A 072 : : 0111010
59 3B 073 &#59; ; 0111011
60 3C 074 &#60; < 0111100
61 3D 075 &#61; = 0111101
62 3E 076 &#62; > 0111110
63 3F 077 &#63; ? 0111111
64 40 100 &#64; @ 1000000
65 41 101 &#65; A 1000001
66 42 102 &#66; B 1000010
67 43 103 &#67; C 1000011
68 44 104 &#68; D 1000100
69 45 105 &#69; E 1000101
70 46 106 &#70; F 1000110
71 47 107 &#71; G 1000111
72 48 110 &#72; H 1001000
73 49 111 &#73; I 1001001
74 4A 112 &#74; J 1001010
75 4B 113 &#75; K 1001011
76 4C 114 &#76; L 1001100
77 4D 115 &#77; M 1001101
78 4E 116 &#78; N 1001110
79 4F 117 &#79; O 1001111
80 50 120 &#80; P 1010000
81 51 121 &#81; Q 1010001
82 52 122 &#82; R 1010010
83 53 123 &#83; S 1010011
84 54 124 &#84; T 1010100
85 55 125 &#85; U 1010101
86 56 126 &#86; V 1010110
87 57 127 &#87; W 1010111
88 58 130 &#88; X 1011000
89 59 131 &#89; Y 1011001
90 5A 132 &#90; Z 1011010
91 5B 133 &#91; [ 1011011
92 5C 134 &#92; \ 1011100
93 5D 135 &#93; ] 1011101
94 5E 136 &#94; ^ 1011110
95 5F 137 &#95; _ 1011111
96 60 140 &#96; ` 1100000
97 61 141 &#97; a 1100001
98 62 142 &#98; b 1100010
99 63 143 &#99; c 1100011
100 64 144 &#100; d 1100100
101 65 145 &#101; e 1100101
102 66 146 &#102; f 1100110
103 67 147 &#103; g 1100111
104 68 150 &#104; h 1101000
105 69 151 &#105; i 1101001
106 6A 152 &#106; j 1101010
107 6B 153 &#107; k 1101011
108 6C 154 &#108; l 1101100
109 6D 155 &#109; m 1101101
110 6E 156 &#110; n 1101110
111 6F 157 &#111; o 1101111
112 70 160 &#112; p 1110000
113 71 161 &#113; q 1110001
114 72 162 &#114; r 1110010
115 73 163 &#115; s 1110011
116 74 164 &#116; t 1110100
117 75 165 &#117; u 1110101
118 76 166 &#118; v 1110110
119 77 167 &#119; w 1110111
120 78 170 &#120; x 1111000
121 79 171 &#121; y 1111001
122 7A 172 &#122; z 1111010
123 7B 173 &#123; { 1111011
124 7C 174 &#124; \ 1111100
125 7D 175 &#125; } 1111101
126 7E 176 &#126; ~ 1111110
127 7F 177 &#127; DEL 1111111

image

The very raw image format is an array of pixels.

A pixel is a picture cell, a raw colored point.

Each pixel is composed by 3 numbers representing the red value, the green value, and the blue value.

It is named RGB (or Digital 8-bit per channel).

It is a 24bits data structure (3 bytes because 3x8bits) :

  • represented with integers : RGB(255, 255, 255)
  • represented with hexadecimals : #FFFFFF

It is named true color and allows 16,777,216 color variations. The human eye can discriminate up to 10 millions colors.

information

An information contained in a data rely on the interpretation context.

For example, the number 20 stored in a data to represent 20 degree. Knowing that the number 20 is for degree (temperature) is not enough to have the information. Is it Celcius or Fahrenheit ? 20°F equal -6.6°C. This is not the same thing in the physical reality.

Other example, a transaction amount. 20 euros is not the same value as 20 dollars.

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