dbms unit 1 - part a questions

7/29/2019 dbms unit 1 - part a questions

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1) Define database & database management:-

Database is a collection of data. It contains about one particular enterprise.

Database management system consists of a collection of interrelated data and a set of programs to

access that data. The primary goal of DBMS is to provide an environment that is both convenient and

efficient to use in retrieving and storing database information.

2)Data abstraction and their types:-

A major purpose of a database system is to provide users with an abstract view of the data.That is, the

system hides certain details of how the data are stored and maintained.

Physical level:- The lowest level of abstraction describes how the data actually stored.The physical level

describes complex low-level data structures in detail.

Logical Level:- It is the next higher level of abstraction that describes what data ares stored in the

database and what relationships exist among those data.

View level:- It is the highest level of abstraction that describes only part of the entire database.

3) Define Instance and schema:-

The collection of information stored in the database at a particular moment is called as Instance of the

database.

The overall design of the database is called the database schema. schema's are changed infrequently, if

at all.

4)Data Models and types:-

A collection of conceptual tools for describing data, data relations, data semantics and consistency

constrains. Entity-relationship model and relational model are the types of data model.

5)Database language:-

A database system provides a data definition language to specify the data base schema and a data

manipulation language to express database queries and updates.

6) Data Definition Language:-

A database schema by a set of definitions expressed by a special language called a Data Definition

Language(DDL)

DDL is a set of SQL commands used to create, modify and delete database structure but not data.

Ex:- Create, Delete, Drop, Alter, Truncate.

7)Data Manipulation Language:-

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

by the appropriate data model.

There are two types:

1) Procedural DMLs: require a user to specify what data are needed and how to get those data.


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2) Declarative DMLs:(Non-procedural) require a user to specify what data are needed without specifying

how to get those data.

8) query Language:-

A query is a statement requesting the retrieval of information. The position of a DML that involves

information retrieval is called a query language.

9) Database Administrator:-

A person who has such central control over the system is called a database administrator. The functions

of a DBA include

@ Schema definition.

@ storage structure and access-method definition.

@ Schema and physical-organization modification.

@ Granting of authorization for data access.

@ routine maintenance.

10) Transaction:-

A transaction is a collection of operations that performs a single logical functions in a database

application. Each transaction is a unit of both atomicity and consistency.

11)Failure recovery:-

A database system must perform failure recover, that it detect system failure and restore the database

to the state that existed prior to occurrence of the failure.

12) Concurrency- control manager:-

concurrency-control manager is responsible to control the interaction among the concurrent

transactions, to ensure the consistency of the database.

13) Functional component of database system:-

The functional component of a database system can be broadly divided into storage manager and the

query processor components.

14) Storage Manager:-

A storage manager subsystem is provides the interface between the low level stored in the database

and the application program and queries submitted to the system.

The storage manager components include:

# Authorization and integrity manager.

# Transaction manager.

# File manager.

# Buffer manager.


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15) Entity-Relationship (E-R)

The entity-relationship data model perceives the real world that consists of a set of basic objects entities

and a relationships among the objects.

16) Entity and Entity set:-

An entity is an object that exists in the real world and is distinguishable from other objects. The

collection of all entities of the same type is an entity set.

17) Relationship AND Relationship set:-

A relationship is associated among several entities and the collection of all relationships of the same

type is a relationship set.

types of relationship: 1)Unary relationship.

2)Binary relationship.

3)ternary relationship.

4) Quaternary relationship.

18) Mapping Cardinalities:

Mapping Cardinalities express the number of entities to which another entity can be associated via a

relationship set.

19) Key and types Key:-

Key:- A key allows as to identify a set of attributes and thus distinguishes entites from each other.

Super Key:- A superkey is a set of one or more attributes that, taken collectively, allow us to identify

uniquely an entity in the entity set.

Primary Key:- A minimal superkey for each entity set among its superkeys; the minimal superkey is

termed the entity set's primarykey.

20) Weak and Strong Entity Set:-

An entity set that does not have sufficient attributes to form a primary key is termed as weak entity set.

An entity set that has a primary key is termed as strong entity set.

21)Specialization and Generalization:-

Specialization and Generalization define a containment relationship between a higher-level entity set

and one more lower-level entity sets.

Specialization:- result taking a subset of a higher-level entity to form a lower-level entity set.

Generalization:- result of taking the union of two or more disjoint entity sets to produce a higher-level

entity set. The attributes of higher-level entity sets are inherited by lower-level entity sets.

22) Aggregation:-

Aggregation is an abstraction in which relationship sets are treated as higher-level entity sets, and


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participate in relationship.

23) Attribute Inheritance:-

A crucial property of the higher and lower-level entities created by specialization and generalization is

attribute inheritance.

24) relational model:-

The relational model was introduced by Dr. E.F.Codd in 1970 and has evolved since then, thought a

series of writings. The relational model represents data n the form of two dimensional tables. Each table

represents some real world entity set manager and thing. The organizational of data into relational

tables is known as the logical view of the data base.

25) Relational data management:-

A relational database management system uses only its relational capabilities to manage the

information in its database.

26) Integrity Constraints:-

Constrains that apply to entity integrity and referential integrity are specifiable by the data language

implemented by the DBMS and not by the statements coded into the application program.

27) Principle Components of Relational Models:-

@ data structure

@ data integrity

@ data manipulation

28) Relational Integrity:-

Integrity constrains provides a means of ensuring that changes made to the database by authorized

users do not result in a loss of data consistency.

There are two types :- Domain constrain and referential constrain.

29)Domain constrain:- It specifies the set of values that can be associated with an attribute. These are

the most elementary form of integrity constrain. They are tested easily by the stream whenever a new

data item is entered into the database.Such constrains also prohibits use of null values for particular

fields.

30)Referential Constrain:- A value that appears in one relation for a given set of attributes also appears

for a certain set of attributes in another relation. This is called referential integrity.

dbms unit 1 - part a questions

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