RDBMS Programming and Technical

Q. Describe the three levels of data abstraction?

A. 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

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RDBMS Other Question
Q. Disadvantage in File Processing System?

A. Data redundancy & inconsistency.
Difficult in accessing data.
Data isolation.
Data integrity.
Concurrent access is not possible.
Security Problems. Q. Define the "integrity rules"

A. 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.