Data INDEPENDENCE is a notion that states that changes in data at one level of a three-tier DataBase Management SYSTEM DESIGN should not affect data at another level. There are two types of data independence:  Physical data independence and Conceptual data independence.

• Physical Data Independence: Any change in the physical location of tables and indexes should have no impact on the conceptual level or the external DISPLAY of data, according to Physical Data Independence. The majority of Database Management Systems offer this data independence, which is straightforward to establish.
• Conceptual Data Independence: Data at the conceptual and external levels must be independent, according to Conceptual Data Independence. Any changes to the conceptual schema should have no effect on the external schema. Changing the appearance of a table by adding or removing features, for example, should have no impact on the user's view of the table. This type of independence, however, is more DIFFICULT to accomplish than physical data independence since changes in conceptual schema are mirrored in the user's view.