As we know, the Basic purpose of a 3-level schema is to achieve the goal of data Independence.
Data independence means independence of the data from the user. Therefore, It follows the 3-level of abstraction (3-schema architecture).
Types of Data Independence
There are two basic types of data independence, As explain below
1. Logical Data Independence
- Logical data independence separates the external level from the logical/conceptual level.
- If any change occurs in the conceptual schema, then it will not affect the user view.
2. Physical Data Independence
Physical data independence separates the physical level (internal) from the conceptual view.
In the same way, if any change is required in the physical schema, then it will not affect the conceptual schema.
i.e., Gmail makes changes in conceptual and physical schema on a regular basis without changing the user view.
Note: Data can be centralized or distributed in database storage.