2. DATABASE
� A database is a collection of interrelated data.
� It can serve multiple applications.
� It is computer based recordkeeping system.
� It not only allows to store but also allows us
modification of data as per requirements.
2
3. FILE SYSTEM
� A file can be understood as a container to store
data in a computer. Files can be stored on the
storage device of a computer system. Contents of a
file can be texts, computer program code, comma
separated values (CSV), etc. Likewise, pictures,
audios/videos, web pages are also files.
� Files stored on a computer can be accessed
directly and searched for desired data.
� But one has to write computer programs for efficient
access of data from files.
3
4. DBMS
� DBMS refers to Database Management System
� It is a software that can be used for creating,
storing, manipulating, maintaining and retrieving
data from database by users or application
programs.
� The DBMS serves as an interface between the
database and end users or application programs.
� Some examples of open source and commercial
DBMS include MySQL, Oracle, PostgreSQL, SQL
Server, Microsoft Access, MongoDB.
4
5. NEED OF DBMS
File system becomes difficult to handle when number
of files increases and volume of data also grows.
Following are some of the advantages of database:
� Database reduces redundancy
Redundancy means same data are duplicated in
different places (files). It removes redundancy as the
data are stored at one place and all the application
refers to the centrally maintained database.
� Database controls inconsistency
Data inconsistency occurs when same data maintained
in different places do not match. By controlling
redundancy, the inconsistency is also controlled.
� Database facilitates sharing of data
Data stored in the database can be shared among
several users.
5
6. NEED OF DBMS
� Database ensures security
Data are protected against accidental or intentional
disclosure to unauthorized person or unauthorized
modification.
� Database maintains integrity
It enforces certain integrity rules to ensure the
validity or correctness of data.
� Database enforces standard
Database is maintained in a standard format which
helps data interchange or migration of data
between two systems.
6
7. KEY CONCEPTS IN DBMS
� Database Schema
▪ Database Schema is the design of a database.
▪ Database schema is also called the visual or logical
architecture as it tells us how the data are organised in
a database.
� Data Constraint
▪ It is certain restrictions or limitations on data to ensure
its validity and consistency.
� Meta-data or Data Dictionary
▪ The database schema along with various constraints on
the data is stored by DBMS in a database catalogue or
dictionary, called meta-data.
▪ A meta-data is data about the data.
7
8. KEY CONCEPTS IN DBMS
� Database Instance
The state or snapshot of the database at any given time
is the database instance
� Database Query
A query is a request to a database for obtaining
information in a desired way.
� Data Manipulation
▪ Modification of database
▪ It consists of three operations viz. Insertion, Deletion or
Updating.
� Database Engine
▪ Database engine is the underlying component or set of
programs used by a DBMS 8
9. RELATIONAL DATA MODEL
� In a relational database model, data is organized
into tables (i.e. rows and columns).
� These tables are also known as relations.
� A row in a table represents relationship among a
set of values.
� A column represents the field/attributes related to
relation under which information will be stored.
� For example: If we want to store the details of
students then Roll_No, Class, Section etc. will be
the column/attributes and the collection of all the
column data will become a Row/Attribute. 9
10. COMPONENTS COMPRISING A TABLE
� Data Item: smallest unit of named data. It represent
one type of information and often referred to as a
field or column information
� Record: collection of data items which represent a
complete unit of information
� Table: collection of all Rows and Columns.
10
11. COMMONLY USED TERMINOLOGIES IN
RELATIONAL DATA MODEL
The Relational Model was developed by E. F. Codd of
the IBM in 1970 and is the most widely used Database
Model.
� Relation / Table
A Relation/Table is a tabular structure arranged in
rows and columns. It has the following properties:
▪ All items in a column are homogeneous i.e. they are of
the same data type
▪ Each column is assigned a unique name and has an
atomic(indivisible) value.
11
12. COMMONLY USED TERMINOLOGIES IN RELATIONAL
DATA MODEL
▪ No attribute can have many data values in one
tuple .
▪ All rows of a relation are distinct i.e. no two identical
rows are present in a relation.
▪ Ordering of rows or columns are immaterial.
▪ A special value “NULL” is used to represent values
that are unknown or non-applicable to certain
attributes.
12
13. COMMONLY USED TERMINOLOGIES IN
RELATIONAL DATA MODEL
� Domain
It is a set of values from which an attribute can take a value in
each row. Usually, a data type is used to specify domain for
an attribute.
� Tuple / Entity / Record
Each row of data in a relation (table) is called a tuple.
� Attribute / Field
The columns of a relation are the attributes which are also
referred as fields.
� Degree
The number of attributes in a relation is called the Degree of
the relation
� Cardinality
The number of tuples in a relation is called the Degree of the
relation 13
14. DATABASE TABLE/RELATION
ROLL NAME CLASS
01 VIJETHA 12
02 SINDHU 11
03 GAUTHAMI 12
14
STUDENT
Rows
/
Tuples
Table
/
Relation
Data Item
Records
Table/Relation
Name
Columns / Attributes
15. KEYS IN A RELATIONAL DATABASE
The tuples within a relation must be distinct. It
means no two tuples in a table should have same
value for all attributes. That is, there should be at
least one attribute in which data are distinct
(unique) and not NULL. That way, we can uniquely
distinguish each tuple of a relation. So, relational
data model imposes some restrictions or
constraints on the values of the attributes and how
the contents of one relation be referred through
another relation. These restrictions are specified
through different types of keys.
15
16. KEYS IN A RELATIONAL DATABASE
� Primary Key
▪ A set of one or more attribute(s) that can uniquely
identify a record in the relation is called Primary
Key.
▪ There can be only one primary key in a table.
▪ A primary key accepts only distinct (non-duplicate)
values and cannot be left blank.
▪ E.g. Student ID No, Student Admission No, Aadhar
Card No etc. qualifies as Primary Key as the values
of all these are unique.
16
17. KEYS IN A RELATIONAL DATABASE
� Candidate Key
▪ A table can have one or more attributes that takes
distinct values. Any of these attributes can be used
to uniquely identify the tuples in the relation. Such
attributes are called candidate keys.
▪ A Primary Key is one of the candidate keys.
▪ A table may have more than one candidate keys
but definitely has one and only one primary key.
17
18. KEYS IN A RELATIONAL DATABASE
� Candidate Key
STUDENT
� In the above given table Stud_ID, Roll_No, Email_ID
can uniquely identify a row in the table and hence they
are candidate keys.
18
Stud_ID Roll_No Name Stream Email_ID
200601 01 Nikitha Science nk@gmail.com
200607 03 Srinidhi Commerce ss@gmail.com
200647 18 Sahana Science sk@gmail.com
Candidate Keys
19. KEYS IN A RELATIONAL DATABASE
� Composite Primary Key
▪ If no single attribute in a relation is able to uniquely
distinguish the tuples, then more than one attribute are
taken together as primary key. Such primary key
consisting of more than one attribute is called
Composite Primary key.
▪ Here a composite Primary Key (CLASS,SECTION) can
be formed together as either of these column in
isolation cannot be used to uniquely identify each row in
the table.
19
CLASS SECTION TOT_STRENGTH
X A 32
XII A 30
XII B 28
20. KEYS IN A RELATIONAL DATABASE
� Alternate Keys
▪ Only one of the Candidate keys is selected as the
primary key of a table. All other candidate keys are
called Alternate keys.
▪ A Candidate Key which is not a primary key is an
Alternate Key.
▪ Candidate Keys – Primary Key = Alternate Key(s).
▪ E.g. In the table STUDENT mentioned in Page No.
18, if Stud_ID is selected as the Primary Key then
Roll_No and Email_ID will become the Alternate
Keys.
20
21. KEYS IN A RELATIONAL DATABASE
� Foreign Key
▪ A foreign key is used to represent the relationship
between two tables.
▪ It is a non-key attribute whose value is derived from
the Primary key of another table.
▪ Foreign key column will check for the presence of
value in Primary key of another table, if present then
only entry will be allowed otherwise data will be
rejected.
21
22. KEYS IN A RELATIONAL DATABASE
▪ In some cases, foreign key can take NULL value if it
is not the part of primary key of the foreign table.
▪ The table containing the foreign key is called the
child table, and the table containing the candidate
key is called the referenced or parent table.
22
23. KEYS IN A RELATIONAL DATABASE
23
ORDERS
CUSTOMER
▪ From the above given tables we can observe that the CUST_ID column
of ORDERS table is deriving its value from CUST_ID of CUSTOMER
table. So we can say that the CUST_ID of ORDERS table is a foreign key
whose value is dependent upon the Primary key column CUST_ID of
table CUSTOMER.
ORDER_ID ORDER_NO CUST_ID
1 1255 3
2 1690 3
3 1810 2
4 2210 1
CUST_ID NAME ADDRESS
1 HECTOR MADRID
2 MITCHELLE LONDON
3 AUGUSTA COLARADO
Child Table
Parent
Table
24. REFERENTIAL INTEGRITY
� The property of a relational database which ensures
that no entry in a foreign key column of a table can
be made unless it matches a primary key value in the
corresponding column of the related table is called
referential integrity.
� It also ensures that the user don’t accidentally delete
or change the related data.
� Referential integrity can be applied when:
▪ The master table’s column is a Primary Key or has a
unique index.
▪ The related fields have the same data type.
▪ Both tables must belong to the same database. 24
25. REFERENTIAL INTEGRITY
� The following rules must be followed if the referential
integrity is enforced using Foreign Key:
▪ We cannot enter a value in Child Table which is not
present in Master Table’s Primary key column.
However, NULL values can be entered in foreign key.
▪ We cannot delete a record from Master Table if
matching record exists in related table/Child Table.
▪ We cannot modify or change the Primary Key value
in Master table if its matching record is present in
related table/Child Table.
25
