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Data Abstraction is the process of hiding the background and implementation details that are irrelevant to the end-user. Data abstraction allows the user to view only the essentialinformation. Using data abstraction, the user can easily interact with the database, without knowing the database implementation. information. Using data abstraction, the user can easily interact with the database, without knowing the database implementation. knowing the database implementation.

There are three levels of database abstraction.
They are:
i. Physical level
The Physical level is the lowest data abstraction level. It deals with the physical storage of data in the disks or some other secondary storage devices. It explains the ordering of records on the disks and the different indexing methods used. This level is usually hidden from the application programmers.
ii. Logical Level or Conceptual Level
This level deals with the organization of data (generally in the form of tables). It deals with the attributes and records of the tables, and also the relationship between the tables. Details of the physical level are removed at this level using abstraction. This level is used by Database Administrators and Application programmers.
iii. View level
The View level is the highest level of abstraction. It provides the abstracted view tailored to a user. All the internal implementations of the database are abstracted in this level. The data is presented in a useful form or each user.

The DBMS Two-Tier architecture is similar to the Client-Server model. The user application programs are on the Client side, and the database is one the server side. Here, the user application can directly communicate with the Database Server, by establishing a communication link. The two tier architecture can be understood clearly from the following block diagram.

The DBMS Three-Tier architecture consists of three major components.
They are
a. Client-side application (or) user interface
b. Server-side application
c. Database system
Here, unlike the 2 two tier architecture, the client application cannot directly communicate with the database. Instead, it communicates with the application on the server side, which in turn retrieves the required data from the database.