DBMS Interview Questions and Answers Second 16 to 30

QUESTION 16:

What is an Entity?

ANSWER:

It is a 'thing' in the real world with an independent existence.

QUESTION 17:

What is an Entity type?

ANSWER:

It is a collection (set) of entities that have same attributes.

QUESTION 18:

What is an Entity set?

ANSWER:

It is a collection of all entities of particular entity type in the database.

QUESTION 19:

What is an Extension of entity type?

ANSWER:

The collections of entities of a particular entity type are grouped together into an entity set.

QUESTION 20:

What is Weak Entity set?

ANSWER:

An entity set may not have sufficient attributes to form a primary key, and its primary key compromises of its partial key and primary key of its parent entity, then it is said to be Weak Entity set.

QUESTION 21:

What is an attribute?

ANSWER:

It is a particular property, which describes the entity.

QUESTION 22:

What is a Relation Schema and a Relation?

ANSWER:

A relation Schema denoted by R(A1, A2, ?, An) is made up of the relation name R and the list of attributes Ai that it contains. A relation is defined as a set of tuples. Let r be the relation which contains set tuples (t1, t2, t3, ..., tn). Each tuple is an ordered list of n-values t=(v1,v2, ..., vn).

QUESTION 23:

What is degree of a Relation?

ANSWER:

It is the number of attribute of its relation schema.

QUESTION 24:

What is Relationship?

ANSWER:

It is an association among two or more entities.

QUESTION 25:

What is Relationship set?

ANSWER:

The collection (or set) of similar relationships.

QUESTION 26:

What is Relationship type?

ANSWER:

Relationship type defines a set of associations or a relationship set among a given set of entity types.

QUESTION 27:

What is degree of Relationship type?

ANSWER:

It is the number of entity type participating.

QUESTION 28:

What is Data Storage - Definition Language?

ANSWER:

The storage structures and access methods used by database system are specified by a set of definition in a special type of DDL called data storage-definition language.

QUESTION 29:

What is DML (Data Manipulation Language)?

ANSWER:

This language that enable user to access or manipulate data as organized by appropriate data model.

? Procedural DML or Low level: DML requires a user to specify what data are needed and how to get those data.

? Non-Procedural DML or High level: DML requires a user to specify what data are needed without specifying how to get those data.

QUESTION 30:

What is VDL (View Definition Language)?

ANSWER:

It specifies user views and their mappings to the conceptual schema.