About

A three-valued logic implements a boolean as having three possible values:

• true,
• false
• and some indeterminate third value.

Third value origin

This third value comes in play when you want to retrieve a Boolean from a storage where it may be just inexistant.

For instance, if we want to retrieve the value of a boolean attribute called bool from a JSON

• In this case, the value is true

{
   "bool": true
}

• In this case, the value is false

{
   "bool": false
}

• In this case, the value is unknown / indeterminate and map to a sort of missing value infomation

{
}

Storage

You need only two bit to store this values:

• 00: true
• 01: false
• 10: unknwon (that may internally be rebuild as a null value)

Example

• SQL - Boolean

Documentation / Reference

• wiki/Three-valued_logic