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.
What is DBMS ?
It is a collection of programs that enables user to create and maintain a database. In other words it is general-purpose software that provides the users with the processes of defining, constructing and manipulating the database for various applications.
What is a Database system ?
The database and DBMS software together is called as Database system.
Advantages of DBMS ?
Redundancy is controlled.
Unauthorised access is restricted.
Providing multiple user interfaces.
Enforcing integrity constraints.
Providing backup and recovery.
Disadvantage in File Processing System ?
Data redundancy & inconsistency.
Difficult in accessing data.
Concurrent access is not possible.
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.
What is System R? What are its two major subsystems ?
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
System Relational Data System.
How is the data structure of System R different from the relational structure ?
Unlike Relational systems in System R
Domains are not supported
Enforcement of candidate key uniqueness is optional