DBMS Question & Answer ( Short )

What is a database?

A DBMS is a complex software system that is used to manage, store and manipulate

data and metadata used to describe the data.

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What is a key? What are different keys in database?

A key is nothing but a attribute or group of attributes. They are used to perform

Some specific operation depending on their operation. The keys are classified

Into primary key, secondary key, alternative key super key, candidate key, compound

Or concatenated or composite key.

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What is a primary key?

Primary key: an attribute to identify a record uniquely is considered to be

Primary key. For e.g. in the student table student_no is the primary key because it

Can be used to identify unique record or unique student.

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What is a secondary key?

An attribute used to identify a group of records satisfying a given condition is

Said to be a secondary key.in the employee table designation is a secondary key

Because more than one employee can have the same designation.

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What is a candidate key?

Register no usually allotted in the exams is also unique for each student in that

case for identifying a student uniquely either student_no or register_no can be

used. Here two different candidates are contesting for primary key post. Any of

them can be selected as primary key.

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What is an alternate key?

If any one of the candidate keys among the different candidate keys available is

Selected as primary key then remaining keys are called alternate key.

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What is a super key?

With primary key if any other attribute is added then that combination is called

Super key in other words, primary key is the minimum possible super key.in the

Student table student_no+student_name is one the super key.

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What is a composite key?

if the primary key is combination of more than one key then it is Calls the

Composite key.in the table called marks student_no+subject is the composite key.

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What is a relation?

a relation consists of a homogeneous set of tuples.

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What is a table?

It is the representation of a relation having records as rows and attributes as Columns.

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what is an attribute?

an object or entity is characterized by its properties or attributes.

In relational database systems attributes corresponds to fields.

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What is Data Model?

A collection of conceptual tools for describing

data, data relationships data semantics and constraints.

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What is E-R model?

This data model is based on real world that consists

of basic objects called entities and of relationship Among these objects.

Entities are described in a database by a set of attributes.

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What is a domain?

the set of allowable value for the attribute is the domain of the attribute.

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What is a tuple?

Tuples are the members of a relation. An entity type having attributes can be

Represented by set of these attributes called tuple.

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What is a selection?

An operation that selects only some of the tuples in the relation is known as

Selection operation. The selection operation yields a horizontal subset of a Given relation.

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What is a join operation?

The join operation allows the combination of two relations to form a new Relation.

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What are base operations in relational algebra?

Union :

The term of the relation as performed by combining the tuples from one

Relation with those a second relation to produce a third Relation. Duplicate tuples are eliminated. The relation must be union Compatible.

Difference :

the difference of two relations is a third relation having tuples that occur in

the first relation but not in the second relation.

Intersection :

the intersection operation selects the common tuples from the two relations.

Cartesian product :

the Cartesian product of two relations is the concatenation of tuples belonging

to the two relations. A new resultant scheme is created consisting of

concatenation of all possible combination of tuples.

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What are different DBMS facilities?

How many types of facilities are provided by a DBMS?

1) The data definition facility or data definition language (DDL)

2) The data manipulation facility or data manipulation language (DML)

3) The data control facility (DCL)

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What is data definition language?

Data scheme is specified by a set of definitions which are expressed b a special

Language called a DDL.

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what is a data directory or data dictionary?

the result of compilation of DDL statements is a set of tables which are stored

in a special file called data dictionary or data directory.

a data directory is a file that contains metadata i.e. data about data. This file

is consulted before actual is read or modified in the database system.

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What is a DML?

A DML is a language that enables users to access or manipulate data as organized

by the appropriate data model. There are basically two types:

1) Procedural DML require a user to specify what data is needed and how to get it.

2)non procedural DML require a user to specify what data is needed without

specifying how to get it.

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what is a query?

a query is a statement requesting the retrieval of information.

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what is a query language?

the portion of DML that involves information retrieval is called a query

language.

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what are the advantages of DBMS?

reduction of redundancies, integrity, security, conflict resolution, data

independence, shared data, data quality enhanced.

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What is a SQL?

structured query language(SQL) originated in 1974 at IBM.SQL was the data

definition and manipulation language.

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What are the features of SQL?

portability, client server architecture, dynamic data definition, multiple views of

data, complete data base language, interactive, high level structure and SQL

standards.

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How SQL organizes the data?

SQL organizes data as databases, tables, indexes, views.

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What is data definition?

SQL lets a user to define the data structure and relationship at the stored data.

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What is data retrieval?

Allows a user or an application program to retrieve the stored data.

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what is data sharing?

data can be shared by more than one user.

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What are data manipulation operations?

remove, append, create, delete.

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Data definition is done through which statement?

data definition in SQL is via the create statement. The statement can be used to

create a table, index or view.

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what is the command to alter the structure of the table?

the definition of the existing relation can be altered by using ALTER

statement. This statement allows a new column to be added to an existing

relation.

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What is a view?

It is an object of SQL. A query can be defined, stored and named. This is called

view.

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what is a first normal form?

a relation which contains no multi valued attributes.

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what is a second normal form?

a relation is in second normal form for if it is first normal form and every

non key attribute is fully functionally dependent on primary key.

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what is a third normal form?

a relation is in third normal form if for every functional dependency F : x-> y is a D key.

What is BCNF?

Boyce-code normal form.

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What is fifth normal form?

a relation which eliminates join dependencies.

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What is an Entity?

An Entity is a Think about which we store data.

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What is an Entity type?

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

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What is an Entity set?

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

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List out Entity :

•          Super Entity

•          Sub Entity

•          Strong Entity

•          Weak Entity

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What Is Strong Entity ?

An entity which is independent means it is not dependent on other entity.

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What is Weak Entity ?

A weak entity set is an entity set that does not contain sufficient attributes to uniquely identify its entities.

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What is Sub Entity ?

An Entity which is part of super entity Is called Sub Entity.

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What is Super Entity ?

An entity teach is main thing is called super entity. E.g. My HOD.

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List out Attributes :

•          Simple attribute

•          Composite attribute

•          Derived attribute

•          Single-value attribute

•          Multi-value attribute

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Types of Attributes :

• Simple attribute − The attributes which cannot be divided into smaller subparts are called simple or atomic attributes. For example, age of employee entity.

• Composite attribute − Attribute can be subdivided into two or more other Attribute.

For Example, Name can be divided into First name, Middle name and Last name.

• Derived attribute − Attributes derived from other stored attribute.

For example age from Date of Birth and Today’s date.

• Single-value attribute − Single-value attributes contain single value.

For example − Social_Security_Number.

An attribute, that has a single value for a particular entity. For example, age of a employee entity.

• Multi-value attribute − An attributes that may have multiple values for the same entity.

For example, colors of a car entity.

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What is the command to delete a record in the table?

DELETE.

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what is the command to delete a table?

DROP TABLE.

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What is the command to insert a record?

INSERT INTO.

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What is the command to alter table values in SQL?

UPDATE.

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what is time stamping?

in the time stamping based method, a serial order is created among the concurrent

Transactions by assigning to each transaction a unique no decreasing numbers. You

will be allocating fixed time for each transaction.

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what is data base schema?

it is the description of the database i.e. its data structure and not the detail.

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what is a self-join?

joining the table to the same table.

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what are the different aggregate functions in SQL?

AVG(),MIN(),MAX(),COUNT(),SUM().

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what is data integrity?

data must satisfy the integrity constraints of the system.

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what is data independence?

a database system keeps data separate from software data structures.

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what is dead locking?

it is the situation where two transactions are waiting for other to release a

lock on an item.

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what is decryption?

taking encoded text and converting it into text that you are able to read.

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what is a distributed database?

a database in which the data is contained within a number of separate

subsystems usually in different locations.

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what is a conceptual data model?

a conceptual data model is concerned with the general description of the data

base without concern for how the data may be organized.

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What is cardinality?

The no of instances of each entity involved in an instance of a relation of a

relationship describe how often an entity can participate in relationship. ( 1: 1, 1: many, many: many)

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