What is data abstraction? Describe the levels briefly. DBMS

Data Abstraction: Different users require different view of the database which is useful and necessary to them. This is data abstraction by which we abstract useful data from a database for a particular type of users to use. 

There are 3 levels of data abstraction, those are as follows;

  1. Physical Level: The lowest level of abstraction describes how the data are actually stored. The physical level describes complex low level data structures. 
  2. Logical Level: This level of abstraction describes what data are stored in the database and what relationships exist among those data. Thus it also describe structures but separating them in small parts.
  3. View Level: This level represents only a part of the entire database. Even though logical level is simpler than physical level, view level is required because a database may have tons of data all of which are not useful to all users.
What are instances and schema? DBMS

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