Physical vs Logical Data Independence: Know the Difference between Physical and Logical Data Independence
Both of these are types of data independence in a Database Management System, commonly abbreviated as DBMS. However, there is a primary difference between Physical and Logical Data Independence. In this article, we are going to discuss the same. But before we do that, let us know a bit more about what data independence actually is.
What is Data Independence?
It is basically a property of the DBMS that lets a user change the schema of a Database at any given database system level without having to change the higher/ next level Database schema. The process of data independence assists the users to segregate the data from those programs that utilise it.
This stored data is then used for presentation as well as computing. Thus, data independence is a very crucial part and essential function in many systems, and it forms an essential component.
Nevertheless, data independence is of two major types, namely physical data independence and logical data independence. Let us know a bit more about these two now.
What is Physical Data Independence?
It is mainly used when we want to separate the conceptual level data from the physical/ internal levels. Physical data independence is fairly easy to achieve. It helps a user change the storage structure physically of the devices that have a direct effect on their conceptual schema.
Here are a few examples of changes made under the physical data independence:
- Modification of indexes.
- Altering the access method.
- The process of switching to a different data structure.
- Modification of the file organization technique in a DB (Database).
- Using some new storage device, such as Magnetic Tapes or Hard Drive.
- For altering the hashtag algorithms or compression techniques.
- Changing the database location. For example, from C to D drive.
What is Logical Data Independence?
It is mainly used when we want to change the conceptual scheme, but we don’t want to change the External programs or APIs and external views.
Here are a few examples of changes made under the Logical Data Independence:
- For deleting, modifying, or adding a new attribute. This relationship or entity is possible even if we don’t rewrite the existing apps or programs.
- When we are merging two of the records into a single one.
- When we are trying to break an existing record. Meaning, when we are dividing any record into further two records.
Difference between Physical and Logical Data Independence
Let us talk about the differences between Physical and Logical Data Independence.
| Parameters | Physical Data Independence | Logical Data Independence |
| Basics | Physical data independence is concerned mainly with how a set of data/ info gets stored in a given system. | Logical data independence is concerned mainly with the changing definition of the data in a system or its structure as a whole. |
| Ease of Retrieving | We can easily retrieve it. | Retrieving is very difficult because the data mainly depends on its logical structure and not its physical location. |
| Ease of Achieving | Achieving physical data independence is much easier as compared to logical data independence. | Achieving logical data independence is more difficult as compared to physical data independence. |
| Degree of Changes Required | The changes made at the physical level need not be made at the application level. | Any changes made at the physical level need to be made at the application level as well. |
| Internal Modification | We may or may not need the modifications at the internal level for improving the performance of a system’s structure. | Making modifications at the logical level is a prerequisite whether we want to change the database structure or not. |
| Type of Schema | The internal schema is the primary concern. | The conceptual schema is the primary concern. |
| Examples | For example, altering the compression techniques, storage devices changes, and changes in the hashing algorithms. | For example, adding, deleting, or modifying any attribute in a system. |
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