There are two types of data independence:
- Physical Data Independence: It refers to the ability to modify the physical schema without affecting the conceptual schema or the external schema. In other words, physical data independence allows us to change the storage structures, file organization, or indexing methods without affecting the user programs or applications.
For example, if a database is initially stored on a magnetic disk, it can be later changed to an optical disk or solid-state drive, without changing the external or conceptual schema.
- Logical Data Independence: It refers to the ability to modify the conceptual schema without affecting the external schema or the physical schema. In other words, logical data independence allows us to modify the logical structure of the data, such as adding or deleting attributes, changing the data types, or altering the relationships between entities, without affecting the user programs or applications.
For example, if a database is initially designed with a single entity, it can be later modified to include multiple entities and relationships, without changing the external or physical schema.
Data independence is important because it allows the database designer to modify the data storage or organization without affecting the user programs or applications, which saves a lot of time and effort. Additionally, it allows for the separation of concerns between the database designer and the application developer, which can lead to better software design and maintenance.