DBMS Basics - Interview Questions and Answers
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
Its two subsystems are
- Research Storage
- 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
- Enforcement of entity integrity is optional
- Referential integrity is not enforced
What is Data Independence?
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
What is a view? How it is related to data independence?
A view may be thought of as a virtual table, that is, a table that does not really exist
in its own right but is instead derived from one or more underlying base table. In
other words, there is no stored file that direct represents the view instead a
definition of view is stored in data dictionary.
Growth and restructuring of base tables is not reflected in views. Thus the view can
insulate users from the effects of restructuring and growth in the database. Hence
accounts for logical data independence.