According to Eastern philosophy, every substance in the world consists of 5 elements -- wood, fire, earth, gold, water, and in that order. The relationships of 5 elements are generation, mutual generation and mutual restrain. The order of generation is: wood, fire, earth, gold, water; the order of mutual generation: wood generates fire, fire generates earth, earth generates gold, gold generates water, water generates wood; the order of mutual restrain: water restrains fire, fire restrains gold, gold restrains wood, wood restrains earth, earth restrains water.
You can see clearly the relationship from following illustration:
Relationship of 5-element can be demonstrated in line-up too:
Equipment, pet and map also have 5-element attribute. Make use of it, you will get twice the result with half the effort. In addiction, composing a new pet and amalgamation in the Oven of Heaven & Earth have something to do with 5-element.