In a constraint-satisfaction problem (CSP), a variable is an entity whose value is selected from a domain. Domains list possible values; constraints restrict which combinations are acceptable. section 3.0
Two examples show how variables model a problem:
- A meeting participant can be a variable; its domain is the hours when that person is available. section 3.0
- An Australian region can be a variable with red, green, and blue as its domain; border constraints prevent adjacent regions from sharing a color. section 3.2
Figure 3.2. In a solution to the Australian map-coloring problem, no two adjacent parts of Australia can be colored with the same color.
The map illustrates the adjacency condition that constrains region variables. section 3.2
