1: What is database?
ANSWER:
A database is a logically coherent collection of data with some inherent
meaning, representing some aspect of real world and which is designed, built
and populated with data for a specific purpose.
2:What is DBMS?
ANSWER: Redundancy is controlled.
Unauthorized access is restricted.
Providing multiple user interfaces.
Enforcing integrity constraints.
Providing backup and recovery.
3:What
is a Database system?
ANSWER:
The database and DBMS software together is called as Database system.
4:Disadvantage in File Processing System?
ANSWER:
Data redundancy & inconsistency.
Difficult in accessing data.
Data isolation.
Data integrity.
Concurrent access is not possible.
Security Problems. .
5:Describe the three levels of data
abstraction?
ANSWER:
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.
6:Define the "integrity rules"
ANSWER:
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.
7:What
is extension and intension?
ANSWER:
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.
8:What is System R? What are its two major
subsystems?
ANSWER:
System R was designed and developed over a period of 1974-79 at IBM San Jose
Research Center . It is a prototype and its purpose was to demonstrate that it
is possible to build a Relational System that can be used in a real life
environment to solve real life problems, with performance at least comparable
to that of existing system.
Its two subsystems are
Research Storage
System
Relational Data System.
9:How is the data structure of System R
different from the relational structure?
ANSWER:
Unlike Relational systems in System R
Domains are not supported
Enforcement of candidate key uniqueness is
optional
Enforcement of entity integrity is optional
Referential integrity is not enforced
10:What is Data Independence?
ANSWER:
Data independence means that ?the application is independent of the storage
structure and access strategy of data?. In other words, The ability to modify
the schema definition in one level should not affect the schema definition in
the next higher level.
Two types of Data Independence:
Physical Data Independence : Modification in physical level should not affect
the logical level.
Logical Data Independence : Modification in logical level should affect the
view level.
NOTE: Logical Data Independence is more
difficult to achieve