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Database/DBMS Interview Questions And Answers - Part VI.

26)  What Is An Entity, Entity Type & An Entity Set?

Answer: Entity is a 'thing' in the real world with an independent existence. An entity is something which is described in the database by storing its data, it may be a concrete entity a conceptual entity.
For Example: Every person in a college is an entity, Every room in a college is an entity.

Entity type is a collection (set) of entities that have same attributes. Entities with the same basic attributes are grouped or typed into an entity type. For Example: EMPLOYEE and PROJECT.

Entity set is a collection of all entities of particular entity type in the database. Each entity type will have a collection of entities stored in the database, this is called entity set.
Example: Consider 3 employees : Rahul, Ajay & Rohit.
  • Rahul, Ajay & Rohit are each categorized as Entity.
  • Employee will be the Entity type.
  • Entity set will be {Rahul, Ajay, Rohit} - i.e. set of instances of entity.

27) What Is An Attribute? Also Define What Is A Domain?

Answer: Attribute is a particular property, which describes the entity. Attribute will have a name and a value for each entity. Attributes are also called columns or fields in DBMS.
A domain defines a set of permitted values for a attribute or a set of allowable value for an attribute defines the domain of that attribute.

  • Colour is an attribute.
  • Domain of Colour attribute would be {Blue, Green, Violet, yellow, Red, Black, White, Orange….}

28) What Are The Different Types Of Attributes In DBMS?

Answer: The three different types of attributes in DBMS are:
  • Simple
  • Composite
  • Multi-Valued.

29) Differentiate Between Simple, Composite & Multi-Valued Attributes In DBMS?


Simple attribute is one in where each entity has a single atomic value for the attribute.
For example, SSN, Sex, Title.

Composite attribute is one where an attribute may be composed of several components.
For example:
Address (Flat No., Wing No., Building No., Street, City, State, Pin code, Country), or Name(First Name, Middle Name, Last Name).

Composition may form a hierarchy where some components are themselves composite.

Multi-Valued attribute is one where an entity may have multiple values for that attribute.
For example, Color of a CAR or Previous Degrees of a STUDENT. Denoted as {Color} or {Previous Degrees}.
In general, composite and multi-valued attributes may be nested arbitrarily to any number of levels, although this is rare.
For example, Previous Degrees of a STUDENT is a composite multi-valued attribute denoted by { Previous Degrees (College, Year, Degree, Field) }
Multiple Previous Degrees values can exist. Each has four subcomponent attributes: College, Year, Degree, Field.

30) What Are Relation Schema & 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 (rows). Let r be the relation which contains set tuples (t1, t2, t3... tn). Each tuple (row) is an ordered list of n-values t= (v1, v2... vn).

A relation schema is a named relation defined by a set of attribute and domain name pairs. A relational database schema is a set of relation schemas, each with a distinct name.

Relations are also called as tables in DBMS.


31) What Is Degree Of A Relation?
32) Discuss The Properties Of A Relation?
33) What Is Relationship, Relationship Type & Relationship Set?
34) What Is Degree Of Relationship Type?
35) What Is A Recursive Relationship Type?

36) What Is An Extension Of Entity Type?
37) What Is Weak Entity Set?
38) What Is An Entity? Differentiate Between Strong & Weak Entity?
39) What Is An Attribute? What Are The Types Of Attributes?
40) Differentiate Between The Different Types Of Attributes?

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