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