Data independence is a database management system (DBMS) characteristic that lets programmers modify information definitions and organization without affecting the programs or applications that use it. Such property allows various users to access and process the same data for different purposes, regardless of changes made to it.
A database containing patient information, for example, could serve various purposes. A hospital’s billing department can use the data to obtain patients’ charges, discounts, and insurance details. On the other hand, the food services department would need the same data to see the patients’ nutritional requirements. How each department uses the data should not affect the stored information regardless of the changes it undergoes, such as where the patient details are stored or how they are labeled.
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Simply put, data independence helps administrators separate information from the applications and programs that use it. As such, programmers don’t need to modify their source codes every time changes to the data characteristics are made. This property helps save time and other resources, and most importantly, minimizes errors.
You will find two types of answers when you dig deeper into the question, “What is data independence?” These refer to physical and logical data independence. But it’s essential to get acquainted with the levels or schema of a database first to understand these types.
Database Levels or Schema
In our patient database example, the different database levels would look like this:
The first level is the physical schema, which refers to how the data is stored, indexed, and labeled. Next is the conceptual level, the layer that contains the information or concepts and their relationships with one another. The medicines, treatments, and other hospital items used by the patients and their corresponding prices are examples.
Last comes the external level, also referred to as the “view schema.” It is the part of the database that a particular user may be most interested in. The hospital’s food service department, for example, would be interested in information on patients’ diagnoses, nutritional needs, and room numbers, to name a few. On the other hand, the billing department would be interested in the patients’ insurance, discount, and similar details. Note that a single database can be externally viewed in more than one way.
Types of Data Independence
Now that you know the different ways to view a database, let us further answer “What is data independence?” by understanding its two types.
Physical Data Independence
Physical data independence refers to the ability to change the data’s physical structure without affecting the conceptual level. Physical changes include using a new storage device or moving the database’s location, changing the data structure, or altering indexes to speed up data retrieval.
The patient database in our example could be moved from drive C to drive D, but the conceptual schema and external views remain unchanged because of physical data independence.
Logical Data Independence
Logical data independence, on the other hand, allows users to change the conceptual schema without changing the external views. For example, the hospital billing department could add a column to the database table for each patient’s insurance policy number. Having logical data independence means that the view of the food services department and other users are not changed even though modifications were made to the conceptual level.
With fierce competition between programs, apps, and other data-reliant products, it’s crucial to perform internal changes without affecting the end-user view and experience. That is with data independence. With it, database management is more efficient and less prone to error.