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Interview Questions - DBMS Basics

5.
What are the disadvantage in File Processing System?
  1. Data redundancy and inconsistency.
  2. Difficult in accessing data.
  3. Data isolation.
  4. Data integrity.
  5. Concurrent access is not possible.
  6. Security Problems.
6.
Describe the three levels of data abstraction?
The are three levels of abstraction:
  1. Physical level: The lowest level of abstraction describes how data are stored.
  2. Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data.
  3. View level: The highest level of abstraction describes only part of entire database.
7.
Define the "integrity rules"?
There are two Integrity rules.
  1. Entity Integrity: States that "Primary key cannot have NULL value"
  2. Referential Integrity: States that "Foreign Key can be either a NULL value or should be Primary Key value of other relation.
8.
What is extension and intension?
  1. Extension: It is the number of tuples present in a table at any instance. This is time dependent.
  2. Intension: It is a constant value that gives the name, structure of table and the constraints laid on it.
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