# 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 structures
# 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 | `;` | ; | 0111011 | |
| 60 | 3C | 074 | `<` | < | 0111100 | |
| 61 | 3D | 075 | `=` | = | 0111101 | |
| 62 | 3E | 076 | `>` | > | 0111110 | |
| 63 | 3F | 077 | `?` | ? | 0111111 | |
| 64 | 40 | 100 | `@` | @ | 1000000 | |
| 65 | 41 | 101 | `A` | A | 1000001 | |
| 66 | 42 | 102 | `B` | B | 1000010 | |
| 67 | 43 | 103 | `C` | C | 1000011 | |
| 68 | 44 | 104 | `D` | D | 1000100 | |
| 69 | 45 | 105 | `E` | E | 1000101 | |
| 70 | 46 | 106 | `F` | F | 1000110 | |
| 71 | 47 | 107 | `G` | G | 1000111 | |
| 72 | 48 | 110 | `H` | H | 1001000 | |
| 73 | 49 | 111 | `I` | I | 1001001 | |
| 74 | 4A | 112 | `J` | J | 1001010 | |
| 75 | 4B | 113 | `K` | K | 1001011 | |
| 76 | 4C | 114 | `L` | L | 1001100 | |
| 77 | 4D | 115 | `M` | M | 1001101 | |
| 78 | 4E | 116 | `N` | N | 1001110 | |
| 79 | 4F | 117 | `O` | O | 1001111 | |
| 80 | 50 | 120 | `P` | P | 1010000 | |
| 81 | 51 | 121 | `Q` | Q | 1010001 | |
| 82 | 52 | 122 | `R` | R | 1010010 | |
| 83 | 53 | 123 | `S` | S | 1010011 | |
| 84 | 54 | 124 | `T` | T | 1010100 | |
| 85 | 55 | 125 | `U` | U | 1010101 | |
| 86 | 56 | 126 | `V` | V | 1010110 | |
| 87 | 57 | 127 | `W` | W | 1010111 | |
| 88 | 58 | 130 | `X` | X | 1011000 | |
| 89 | 59 | 131 | `Y` | Y | 1011001 | |
| 90 | 5A | 132 | `Z` | Z | 1011010 | |
| 91 | 5B | 133 | `[` | [ | 1011011 | |
| 92 | 5C | 134 | `\` | \ | 1011100 | |
| 93 | 5D | 135 | `]` | ] | 1011101 | |
| 94 | 5E | 136 | `^` | ^ | 1011110 | |
| 95 | 5F | 137 | `_` | _ | 1011111 | |
| 96 | 60 | 140 | ``` | ` | 1100000 | |
| 97 | 61 | 141 | `a` | a | 1100001 | |
| 98 | 62 | 142 | `b` | b | 1100010 | |
| 99 | 63 | 143 | `c` | c | 1100011 | |
| 100 | 64 | 144 | `d` | d | 1100100 | |
| 101 | 65 | 145 | `e` | e | 1100101 | |
| 102 | 66 | 146 | `f` | f | 1100110 | |
| 103 | 67 | 147 | `g` | g | 1100111 | |
| 104 | 68 | 150 | `h` | h | 1101000 | |
| 105 | 69 | 151 | `i` | i | 1101001 | |
| 106 | 6A | 152 | `j` | j | 1101010 | |
| 107 | 6B | 153 | `k` | k | 1101011 | |
| 108 | 6C | 154 | `l` | l | 1101100 | |
| 109 | 6D | 155 | `m` | m | 1101101 | |
| 110 | 6E | 156 | `n` | n | 1101110 | |
| 111 | 6F | 157 | `o` | o | 1101111 | |
| 112 | 70 | 160 | `p` | p | 1110000 | |
| 113 | 71 | 161 | `q` | q | 1110001 | |
| 114 | 72 | 162 | `r` | r | 1110010 | |
| 115 | 73 | 163 | `s` | s | 1110011 | |
| 116 | 74 | 164 | `t` | t | 1110100 | |
| 117 | 75 | 165 | `u` | u | 1110101 | |
| 118 | 76 | 166 | `v` | v | 1110110 | |
| 119 | 77 | 167 | `w` | w | 1110111 | |
| 120 | 78 | 170 | `x` | x | 1111000 | |
| 121 | 79 | 171 | `y` | y | 1111001 | |
| 122 | 7A | 172 | `z` | z | 1111010 | |
| 123 | 7B | 173 | `{` | { | 1111011 | |
| 124 | 7C | 174 | `|` | \| | 1111100 | |
| 125 | 7D | 175 | `}` | } | 1111101 | |
| 126 | 7E | 176 | `~` | ~ | 1111110 | |
| 127 | 7F | 177 | `` | DEL | 1111111 | |
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# 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.
# tree vs graph
Difference Between Tree and Graph
| Basis for comparison | Tree | Graph |
|---|---|---|
| Path | Only one between two vertices. | More than one path is allowed. |
| Root node | It has exactly one root node. | Graph doesn't have a root node. |
| Loops | No loops are permitted. | Graph can have loops. |
| Complexity | Less complex | More complex comparatively |
| Traversal techniques | Pre-order, In-order and Post-order. | Breadth-first search and depth-first search. |
| Number of edges | n-1 (where n is the number of nodes) | Not defined |
| Model type | Hierarchical | Network |
# 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.