Data independence is ability to change the schema at one level of database system without having to change the schema at the next higher level.
1. Physical data independence : It is ability to change the internal schema without affecting the conceptual or external schema. An internal schema may be changed due to several reasons. The separation of internal schema from conceptual schema facilitates physical data independence. If the same data as before remains in database we should not have to change conceptual schema.
2. Logical data independence : It is ability to change conceptual schema without having to change external schema. The conceptual schema may be changed due to change in constraints or addition of new data item or removal of existing data item from the database. The separation of external level from conceptual level enables the user to make changes at conceptual level without affecting external level.
1. Physical data independence : It is ability to change the internal schema without affecting the conceptual or external schema. An internal schema may be changed due to several reasons. The separation of internal schema from conceptual schema facilitates physical data independence. If the same data as before remains in database we should not have to change conceptual schema.
2. Logical data independence : It is ability to change conceptual schema without having to change external schema. The conceptual schema may be changed due to change in constraints or addition of new data item or removal of existing data item from the database. The separation of external level from conceptual level enables the user to make changes at conceptual level without affecting external level.
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