Data Abstraction and Data Independence

DATA ABSTRACTION

Data abstraction can be understood as the process of easing the user interaction with the database by hiding internal irrelevant details from users. The database often is composed of complex data structures and hence the main purpose of the database system has become to provide users with an abstract view of data.

Physical level:

This is the lowest level of abstraction and it describes how the data are actually stored.

Logical level:

The logical level describes what data is stored in the database and what kind of relationships exist among the data. It explains the entire database in terms of a small number of relatively simple structures. It is also known as the middle level of 3-level data abstraction.

View level:

This is the highest level of abstraction. Application programs hide details of data types. Views can also hide information for security purposes. Hence provides simplest user interaction with the database system.

Example: If we are to store students' information in student table then at the physical level these records can be described as blocks of storage such as bytes, gigabytes, terabytes etc. in memory and these details are often hidden from the programmers.At the logical level, these records are described as fields and attributes along with their data types, their relationship can be logically implemented. The programmers generally work at this level because they are aware of such things about database systems.At view level, users are just meant to interact with the system with the help of GUI and enter the details at the screen, they are not aware of how the data is stored and what data is stored. These sort of details are hidden from them.

DATA INDEPENDENCE

Data independence is defined as that the upper levels are unaffected by the changes made in the lower level. In general, the interfaces between the various levels and components should be well defined so that the changes made in certain parts do not influence others much. When a schema at a lower level is changed, just the mappings between this schema and higher-level schemas need to be changed in a database management system that entirely supports data independence. The higher-level schemas remain unchanged. Hence, the application programs do not need to change since they refer to external schemas.

There are two types of data independence:

1. Physical Data Independence
2. Logical Data Independence

Physical Data Independence

It refers that the physical storage structures or devices could be changed without affecting the conceptual schemas. Simply, it can be defined as the ability to modify the physical schema without changing the logical schema. Applications depend on the logical schema.

Logical Data Independence

It refers to the capacity of changing the conceptual schema without having to change the external schemas and their application programs. The conceptual schema can be changed without affecting the existing external schemas.

References:

1. H.F.Korth and A. Silberschatz,"Database system concepts",McGraw Hill,2010
2. A.K.Majumdar and p, Bhattacharaya,"Database Management Systems",Tata McGraw Hill,India,2004
3. F.Korth, Henry. Database System Concepts. 6th edition.
4. Beginners book. Retrieved from beginnersbook.com/levels-of-abstraction/dbms