DATA independence is a concept ACCORDING to which, the change in data at one level of the DBMS three-tier architecture should not influence data at another level. Data independence is of two types of data independence:

• Physical Data Independence: According to Physical Data Independence, any change in the physical location of tables and indexes should have no bearing on the conceptual level or the external display of data. This data independence is simple to achieve and is supported by the majority of Database Management Systems.
• Conceptual Data Independence: According to Conceptual Data Independence, data at the conceptual and external levels must be independent. This means that any changes to the conceptual schema should have no impact on the external schema. Adding or removing CHARACTERISTICS from a table, for EXAMPLE, should have no effect on the user's view of the table. However, unlike physical data independence, this form of independence is more difficult to achieve SINCE changes in conceptual schema are mirrored in the user's view.