Question

How many levels of abstraction a typical DB system should hold? What’s the purpose of each of these abstraction levels?

Answer 1

A typical database system should hold 3 levels of abstraction:

Physical (internal) level is the lowest level of abstraction. It tells how data is stored and organized in memory.

Logical (conceptual) level stores the data as tables and relationships.

View (external) level is basically a user interface. Being the highest level of abstraction, it simplifies the accessibility of the database.