Kerala Plus Two Computer Application Chapter Wise Previous Questions Chapter 8 Database Management System
Plus Two Computer Application Database Management System 1 Mark Important Questions
Question 1.
_____ level describes only a part of a database (MARCH-2016)
a) View
b) Physical
c) Logical
d) high
Answer:
a) View
Question 2.
The number of attributes in a relation is called _____ (MAY-2016)
a) tuple
b) degree
c) cardinality
d) domain
Answer:
b) degree
Question 3.
_______ is the symbol used for select operation in relational algebra. (MAY-2017)
a) σ
b) π
c) ∩
d) ∪
Answer:
a) σ
Plus Two Computer Application Database Management System 2 Marks Important Questions
Question 1.
Is it possible to combine SELECT and of relational algebra into a single statement? Explain with an example. (MARCH-2017)
Answer:
Yes. It is possible to combine SELECT and PROJECT operations of relational algebra into a single statement.
πname(σdesignation = “Manager”(EMPLOYEE))
The above query means select the names of employee whose designation is Manager from the table EMPLOYEE.
Plus Two Computer Application Database Management System 3 Marks Important Questions
Question 1.
Explain different level of data abstraction in DBMS. (MARCH-2017)
Answer:
Sip Levels of Database Abstraction
1) Physical Level (Lowest Level-how) – It describes how the data is actually stored in the storage medium.
2) Logical Level (Next Higher Level-what) – It describes what data are stored in the database.
3) View Level (Highest level-way) – It is closest to the users. It is concerned with the way in which the individual users view the data.
Plus Two Computer Application Database Management System 5 Marks Important Questions
Question 1.
What is relational algebra? Explain any three relational algebra operations. (MARCH-2016)
Answer:
Relational Algebra: It consists of a set of operations that takes one or two relations as input and produces a new relation as a result.
A) SELECT operation
SELECT operation is used to select tuples in a relation that satisfy a selection condition. Greek letter σ (sigma) is used to denote the operation. Syntax,
σcondition (relation)
eg: – σsalary<10000 (EMPLOYEE)-selects tuple whose salary is less than 10000 from EMPLOYEE relation.
B) PROJECT operation
PROJECT operation selects certain columns from the table and discards the other columns. Greek letter π(pi) is used to denote PROJECT operation.
Syntax, πcondition (relation)
eg:- πname,salary (EMPLOYEE) displays only the name and salary of all employees
C) UNION operation
This operation returns a relation consisting of all tuples appearing in either or both of the two specified relations. It is denoted by U. duplicate tuples are eliminated. Union operation can take place between compatible relations only, i.e., the number and type of attributes in both the relations should be the same and also their order.
e.g:-SCIENCE U COMMERCE gives all the tuples in both COMMERCE and SCIENCE.
D) INTERSECTION operation
This operation returns a relation consisting of all the tuples appearing in both of the specified relations. It is denoted by n. It can takes place only on compatible relations,
e.g:- FOOTBALL ∩ CRICKET returns the players who are in both football and cricket teams.
Question 2.
Explain the components of DBMS. (MAY-2016)
Answer:
Components of DBMS are given below.
1) Hardware :- It includes computers such as pc, workstations, Server Computer and super computer, storage devices such as hard disk, network devices such as hubs, switches, routers and other supporting devices used for storage and retrieval.
2) Software:- Collection of programs (DBMS) used to define the structure of a table (DDL), used to add, retrieve, modify and delete records in database (DML), and used to maintain the security to the data (DCL).
3) Data:- It is the main Component for effective storage and retrieval of information data is categorised as fields, records and files.
Fields :- smallest unit of stored data, eg :- Regno, name, batch etc Record:-Collection of related fields eg :-101, Jose, Science
File:- collection of related records
eg :-101, Jose, Science
102, Raju, Commerce
103, Alvis, Humanities etc.
4) Users :- Those who uses the ata
eg :- Data Base Administrator (DBA), Application Programmes, Sophisticated users and end users.
5) Procedures:- These are the steps to follow while using a database.
1) Start and stop the DBMS
2) Log on the DBMS
3) Take backups in regular intervals.
Question 3.
Explain advantages of DBMS over conventional file system. (MAY-2017)
Answer:
Advantages of DBMS
1) Data Redundancy – It means duplication of data. DBMS eliminates redundancy. DBMS does not store more than one copy of the same data.
2) Inconsistency can be avoided – If redundancy occurs there is a chance to inconsistency. If redundancy is removed, then inconsistency cannot occur.
3) Data can be shared – The data stored in the database can be shared by the users or programs.
4) Standards can be enforced – The data in the database follows some standards.
Eg : a field ‘Name’ should have 40 characters long. Some standards are ANSI, ISO, etc.
5) Security restrictions can be applied – The data is of great value so it must be kept secure and private. Data security means the protection of data against accidental or intentional disclosure or unauthorized destruction or modification by unauthorized person.
6) Integrity can be maintained – It ensures that the data is to be entered in the database is correct.
7) Efficient data access – It stored huge amount of data efficiently and can be retrieved whenever a need arise.
8) Crash recovery – Some times all or a portion of the data is lost when a system crashes. A good DBMS helps to recover data after the system crashed.