DBMS Interview Questions and Answers
Question - 31 : - What is an Entity set?
Answer - 31 : -
The entity set specifies the collection of all entities of a particular entity type in the database. An entity set is known as the set of all the entities which share the same properties.
For example, a set of people, a set of students, a set of companies, etc.
Question - 32 : - What is an Extension of entity type?
Answer - 32 : -
An extension of an entity type is specified as a collection of entities of a particular entity type that are grouped into an entity set.
Question - 33 : - What is Weak Entity set?
Answer - 33 : -
An entity set that doesn't have sufficient attributes to form a primary key is referred to as a weak entity set. The member of a weak entity set is known as a subordinate entity. Weak entity set does not have a primary key, but we need a mean to differentiate among all those entries in the entity set that depend on one particular strong entity set.
Question - 34 : - What is an attribute?
Answer - 34 : -
An attribute refers to a database component. It is used to describe the property of an entity. An attribute can be defined as the characteristics of the entity. Entities can be uniquely identified using the attributes. Attributes represent the instances in the row of the database.
For example: If a student is an entity in the table then age will be the attribute of that student.
Question - 35 : - What are the integrity rules in DBMS?
Answer - 35 : -
Data integrity is one significant aspect while maintaining the database. So, data integrity is enforced in the database system by imposing a series of rules. Those set of integrity is known as the integrity rules.
There are two integrity rules in DBMS:
Entity Integrity : It specifies that "Primary key cannot have a NULL value."
Referential Integrity: It specifies that "Foreign Key can be either a NULL value or should be the Primary Key value of other relation
Question - 36 : - What do you mean by extension and intension?
Answer - 36 : -
Extension: The Extension is the number of tuples present in a table at any instance. It changes as the tuples are created, updated and destroyed. The actual data in the database change quite frequently. So, the data in the database at a particular moment in time is known as extension or database state or snapshot. It is time dependent.
Intension: Intension is also known as Data Schema and defined as the description of the database, which is specified during database design and is expected to remain unchanged. The Intension is a constant value that gives the name, structure of tables and the constraints laid on it.
Question - 37 : - What is System R? How many of its two major subsystems?
Answer - 37 : -
System R was designed and developed from 1974 to 1979 at IBM San Jose Research Centre. System R is the first implementation of SQL, which is the standard relational data query language, and it was also the first to demonstrate that RDBMS could provide better transaction processing performance. It is a prototype which is formed to show that it is possible to build a Relational System that can be used in a real-life environment to solve real-life problems.
Following are two major subsystems of System R:
- Research Storage
- System Relational Data System
Question - 38 : - What is Data Independence?
Answer - 38 : -
Data independence specifies that "the application is independent of the storage structure and access strategy of data." It makes you able to modify the schema definition at one level without altering the schema definition in the next higher level.
It makes you able to modify the schema definition in one level should not affect the schema definition in the next higher level.
There are two types of Data Independence:
Physical Data Independence: Physical data is the data stored in the database. It is in the bit-format. Modification in physical level should not affect the logical level.
For example: If we want to manipulate the data inside any table that should not change the format of the table.
Logical Data Independence: Logical data in the data about the database. It basically defines the structure. Such as tables stored in the database. Modification in logical level should not affect the view level.
For example: If we need to modify the format of any table, that modification should not affect the data inside it.
Question - 39 : - What is Join?
Answer - 39 : -
The Join operation is one of the most useful activities in relational algebra. It is most commonly used way to combine information from two or more relations. A Join is always performed on the basis of the same or related column. Most complex queries of SQL involve JOIN command.
There are following types of join:
Inner joins: Inner join is of 3 categories. They are:
- Theta join
- Natural join
- Equi join
Outer joins: Outer join have three types. They are:
- Left outer join
- Right outer join
- Full outer join
Question - 40 : - What is 1NF?
Answer - 40 : -
1NF is the First Normal Form. It is the simplest type of normalization that you can implement in a database. The primary objectives of 1NF are to:
- Every column must have atomic (single value)
- To Remove duplicate columns from the same table
- Create separate tables for each group of related data and identify each row with a unique column