2. Data:Collection of facts in raw form.
Information : Organized and
Processed data is information.
Database : A Collection of data
files in which logically related
information is stored.
Data Base Management System :
A Collection of programs for storing and
retrieving information from the database
is called DBMS.
3. 1.Data Redundancy ( Duplication of Data )
is removed.
2.Data Inconsistency can be controlled.
3.Sharing of Data.
4.Security of Data.
It means data can be protected from an
unauthorized user.
5.Integrity Rules can be applied.
Advantages of DBMS
5. Internal Level
( Physical Level )
The lowest level of database which
is closest to the physical storage.
It describes how the data is
actually stored on the storage
medium.
6. Conceptual Level
The level of database which
describes what data is actually
stored in the database.At this
level the relationship between the
data elements is described.
7. View Level
( External Level )
The level of database which is closest
to the user. It is only concerned with
the way how the data is viewed to
the users .The System is able to
create more than one views for the
end user on the basis of the data
stored.
8. Levels of Data Abstraction
Physical Level
Conceptual Level
View 3
View 2
View 1
9. Data Independence
The ability to modify a scheme
definition at one level without
affecting scheme definition of
next higher level.
It is of two types:
( 1 ) Physical Data Independence
( 2 ) Logical Data Independence
10. ( 1 ) Physical Data Independence:
The ability to modify physical level
without affecting the conceptual
level. In this the application
programs remains the same.
( 2 ) Logical Data Independence:
The ability to modify conceptual
level without affecting the view
level.
11. Relational Data Model
A Data Model where data is organized in the
form of tables. These tables are called relations.
A relation or table is collection of horizontal
rows and vertical columns. This model was
proposed by E.F.Codd of IBM . The data stored
in these relations is logically related.
Advantages :
( 1 ) Easy to understand.
( 2 ) In this model the relationship between
databases is established by data values.
13. Basic Terminology
1. Relation : A relation is a table which a
collection of rows and columns.
2.Domain : It is a pool of values from which
the actual values are taken.
3.Tuple : The horizontal rows of a relation are
called tuples.
4.Attribute : The vertical columns of a
relation are called attributes.
5.Degree of a relation : The total number
of attributes of a relation are termed as
degree of a relation.
14. 6.Cardinality of a relation:The total
number of rows in a relation are known as
cardinality of a relation.
7.View:A view is a virtual table whose
contents are taken from a existing
table(base table) depending upon a condition.
A vies does not have data of its own.
8.Primary Key:A key or a set of keys which
can be used to uniquely identify the tuples
of a relation.
9.Candidate Key:A key or a set of keys
which can be used as a primary key to
identify the tuples of a relation.
15. 10.Alternate Key:
A key or a set of keys which can not be used
to identify the tuples of a relation.
11.Foreign Key:
A key in a relation which can be used to make
a relationship with some other relation and it
appears as a primary key in that relation .
16. Relational Algebra
Operators in Relational Algebra
1. Select Operation :
2. Project Operation :
3. Cartesian Product Operation :
4. Union Operation :
5. Set Difference Operation :
6. Set Intersection Operation :
17. 1. Select Operation :It is a unary operator
which selects the tuples ( horizontal subset )
from a relation that satisfy a given predict or
condition. The selection is denoted by the
symbol sigma ( σ ) .
2. Project Operation :It is a unary operator
which selects the specified attributes ( vertical
subset ) from a relation that satisfy a given
predict or condition. The projection is denoted
by the symbol pi ( π ) .
18. 3. Cartesian Product Operation :
It is a binary operator which yields a new
relation which has a degree ( number of
attributes ) equal to the sum of the degrees of
the two relations operated upon and number
of tuples ( Cardinality ) equal to the product
of the number of tuples of two relations. The
Cartesian Product of two relations A and B is
denoted by A X B .
19. 4. Union Operation :It is a binary operator which
operates on two relations and yields a new relation
that contain tuples from both the relations. The
condition to apply this operator are :
( a ) The two relations A and B must have same
degree.
( b ) The domain of ith attribute of relation A and the
domain of ith attribute of relation B must be same.
All the duplicate tuples are automatically removed
using this operated. The Union Operation of two
relations A and B is denoted by A U B .
20. 5. Set Difference Operation :
It is a binary operator which operates on two
relations and yields a new relation that contain
tuples which are present in first relation but
not in the second table . The condition to apply
this operator is that the two relations A and B
must have same degree. The new relation will
contain the tuples which are present in A but
not in B . The Set difference Operation of two
relations A and B is denoted by A – B.
21. 6. Set Intersection Operation :
It is a binary operator which operates on two
relations and yields a new relation that contain
tuples which are present both the relations.
The condition to apply this operator is that the
two relations A and B must have same degree.
The new relation will contain the common
tuples of A and B . The Set Intersection
operation of two relations A and B is denoted
by A B .
