Bazi has been prominent as early as Song dynasty. It is an authoritative form of fortune telling in China. The rationale of Bazi is in finding the yin-yang balance of the 5 elements of a person. When the yin and yang of the 5 elements are balanced, the person tends to lead a smooth and successful life. When they are out of balance, the person's life tend to have many ups and downs. In other words, Bazi uses the balance of the 5 elements in forecasting a person's destiny.
Bazi has a unique method of analyzing relationships, including family relationship, the number of siblings, personal popularity, marriage and compatibility etc. It can clearly depict the overview of one's life at a macro level, while Ziwei works at a more microscopic level. It can be said that both systems have their advantages and can be used in conjunction to complement each other.