Difference between Physical and Logical Data Independence

Last Updated : 16 Sep, 2024

Data Independence therefore refers to the nature whereby one can change the structure of the database without having to change its implementation or data. There are two types of data independence: The first type is the Physical one as well as the second type is the Logical one. As will be seen, both are meant to shield users from changes in the database but they differ in the kind of changes that they seek to protect the users from. In this article, let’s discuss how physical and logical data independence differ and what perks and pitfalls each approach comes with.

What is Physical Data Independence?

Physical Data Independence speaks to the freedom to alter the physical nature of storing a database without having the same effect on the schema or application layer of the database. It shields the users from alterations of the physical arrangement of information.

Examples of changes under Physical Data Independence

It is by the use of new storage devices like Hard Drive or Magnetic Tapes
Modifying the file organization technique in the Database
Switching to different data structures.
Changing the access method.
Modifying indexes.
To change the compression techniques or hashing algorithms.
To change the Location of the Database from say C Drive to D Drive.

Advantages of Physical Data Independence

Ease of Hardware Upgrades: It helps the database administrator to modify the storage devices or formats without hassling the users.
Improved Performance: Specific solutions are tangled for improvement of physical level without altering application logic.
Cost-Effectiveness: Even certain changes in the data storage, referring to storage (such as compression), may lower expenditures while not affecting applications.

Disadvantages of Physical Data Independence

Limited to Physical Changes: Applicable where only the physical implementation of storage has changed, not the logical organization.
Complex Implementation: While gaining physical independence it may be necessary to utilize such tools and DBMS.

What is Logical Data Independence?

Logical Data Independence is the capability to make changes in the logical schema for example by introducing or deleting new fields without the possibility to change physical schema or user views. This helps in making sure that the application layer is never influenced by the changes of the structure of the database.

Examples of changes under Logical Data Independence

To Add/Modify/Delete a new attribute, entity or relationship is possible without a rewrite of existing application programs.
Merging two records into one.
To break an existing record i.e to divide the record into two or more records.

Advantages of Logical Data Independence

Flexibility in Schema Evolution: From the logical independence we can be in a position to incorporate changes in the business requirements without having to affect user applications.
Enhanced Maintenance: There are certain advantages within this one, which are including easier maintenance since the structural changes do not affect the application.
Long-Term Usability: Makes it possible to develop durable databases that are yet able to change dynamically while the application layer remains static.

Disadvantages of Logical Data Independence

Harder to Achieve: When compared to physical data independence, logical data independence is somewhat more difficult to perform because changes to the logical schema are generally less simple.
Potential Application Issues: when such changes are implemented and not implemented by the recommended standards may result to minor complication when logics based on the data is implemented.

Why is Logical Data Independence Harder to Achieve Compared to Physical Data Independence?

Logical Data Independence is harder to achieve as the application programs are heavily dependent on logical format of the data they access, hence a change in conceptual level might require the change of the entire program application . When it comes to Physical Data Independence, change in the location of database or modifying file organization or use of new storage device etc. Will not require the change at the higher logical levels.