Data normalization has several levels, each with its own rules and criteria. The most common levels are the first, second, and third normal forms (1NF, 2NF, and 3NF), which are based on the concept of functional dependency. A functional dependency is a relationship between two or more attributes, where one attribute determines the value of another attribute. For example, if you have a table with the attributes employee ID, name, and department, then employee ID functionally determines name and department, as each employee ID has a unique name and department.
The higher the level of data normalization, the more refined and normalized the data is. However, higher levels of data normalization may also introduce some trade-offs, such as increased complexity, reduced readability, or reduced flexibility. Therefore, the optimal level of data normalization depends on the nature and purpose of the data, and the balance between the benefits and costs of normalization.