Institute of Information Science - University of Miskolc

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==== Code =====

The mapping of events to messages is called encoding. Messages are recorded in information storage units. The recorded message itself is an //event system//. Encoding is a transformation, based on the mutual and unambiguous correspondence between two event systems.

The tool of encoding is code. A code consists of a finite set of symbols (an alphabet) and coding rules (groups of symbols).

A //code-word// is an elementary message, which consists of a finite number of symbols. The code's syntax is the set of code symbols and the rules for forming code-words.

Encoding changes the information's form, but other information characteristics remain unchanged. There are fixed-length and variable-length codes.

**Basic Types of Codes:**

^ Fixed-length code ^ Variable-length code ^
| Technical codes | Morse code |
| Communication Codes | Human languages |
| Computer codes | Technical languages |

For a fixed (n) length binary code, the number of possible codewords is:

$$ N = 2^n $$

If we form codes from m different symbols, then the number of possible n-length codewords is:

$$ N = m^n $$

The fundamental problem of coding theory is the preservation, security, and maximization of the information content of transmitted messages.


**Morse Code**

//Morse code// is a method of encoding text characters into sequences of //dots// and //dashes// (or short and long signals) that can be transmitted over telecommunication lines or other mediums like light or sound. It was originally developed in the 1830s by **Samuel Morse** and **Alfred Vail** for use in telegraphy.

Key features:
  * **Dot** (.): A short signal or sound.
  * **Dash** (-): A longer signal or sound, typically three times the duration of a dot.
  * **Spacing**:
    * Intra-character space: The space between dots and dashes within a single character (typically silent, as no signal).
    * Inter-character space: The space between characters (equivalent to three dots).
    * Inter-word space: The space between words (equivalent to seven dots).


Examples:
  * **A**: .- (dot-dash)
  * **B**: -... (dash-dot-dot-dot)
  * **C**: -.-. (dash-dot-dash-dot)
  * **SOS**: ... - - - ... (dot-dot-dot, dash-dash-dash, dot-dot-dot) - a universal distress signal.

Example message:
  * **HELLO**: .... . .-.. .-.. - - - (dot-dot-dot-dot, dot, dot-dash-dot-dot, dot-dash-dot-dot, dash-dash-dash)