MORE ABOUT RELATIONAL MODEL
AND NORMAL FORM
RELATIONAL MODEL
The relational model represents the database as a collection of relations. A relation is
nothing but a table of values. Every row in the table represents a collection of related data
values. These rows in the table denote a real-world entity or relationship. The table name
and column names are helpful to interpret the meaning of values in each row. The data are
represented as a set of relations. In the relational model, data are stored as tables.
However, the physical storage of the data is independent of the way the data are logically
organized.
Some popular Relational Database management systems are:
• DB2 and Informix Dynamic Server - IBM
• Oracle and RDB – Oracle
• SQL Server and Access - Microsoft
RELATIONAL MODEL CONCEPTS
1. Attribute: Each column in a Table. Attributes are the properties which define a
relation. e.g., Student_Rollno, NAME,etc.
2. Tables – In the Relational model the, relations are saved in the table format. It is stored
along with its entities. A table has two properties rows and columns. Rows represent
records and columns
represent attributes.
3. Tuple – It is nothing but a single row of a table, which contains a single record.
4. Relation Schema: A relation schema represents the name of the relation with its attributes.
5. Degree: The total number of attributes which in the relation is called the degree of the relation.
6. Cardinality: Total number of rows present in the Table.
7. Column: The column represents the set of values for a specific attribute.
8. Relation instance – Relation instance is a finite set of tuples in the RDBMS
system.Relation instances never have duplicate tuples.
9. Relation key - Every row has one, two or multiple attributes, which is called relation key.
10. Attribute domain – Every attribute has some pre-defined value and scope
which is known as attribute domain.
,Relational Integrity constraints
Relational Integrity constraints is referred to conditions which must be present
for a valid relation. These integrity constraints are derived from the rules in the
mini-world that the database represents.
There are many types of integrity constraints. Constraints on the Relational
database management system is mostly divided into three main categories are:
1. Domain constraints
2. Key constraints
3. Referential integrity constraints
DOMAIN CONSTRAINTS
Domain constraints can be violated if an attribute value is not appearing in the
corresponding domain or it is not of the appropriate data type.
Domain constraints specify that within each tuple, and the value of each attribute
must be unique. This is specified as data types which include standard data types
integers, real numbers, characters, Booleans, variable length strings, etc.
KEY CONSTRAINTS
An attribute that can uniquely identify a tuple in a relation is called the key of the
table. The value of the attribute for different tuples in the relation has to be unique.
REFERENTIAL INTEGRITY CONSTRAINTS
Referential integrity constraints is based on the concept of Foreign Keys. A foreign
key is an important attribute of a relation which should be referred to in other
relationships.
RELATIONAL OPERATIONS
A relational operation involves manipulating one or more tables, or relations , to result in
another table.
Relational Algebra is a procedural query language. Relational algebra mainly provides a
theoretical foundation for relational databases and SQL. The main purpose of using
Relational Algebra is to define operators that transform one or more input relations into an
output relation. Given that these operators accept relations as input and produce relations
as output, they can be combined and used to express potentially complex queries that
transform potentially many input relations (whose data are stored in the database) into a
single output relation (the query results). As it is pure mathematics, there is no use of
English Keywords in Relational Algebra and operators are represented using symbols.
Fundamental Operators
Thes basic/fundamental operators used in Relational Algebra.
Selection(σ)
Projection(π)
Union(U)
Set Difference(-)
Set Intersection(∩)
Rename(ρ)
Cartesian Product(X)
, Selection(σ): It is used to select required tuples of the
relations. Example:
For the above relation, σ(c>3)R will select the tuples which have c more than 3.
Note: The selection operator only selects the required tuples but does not display them. For
display, the data projection operator is used.
Select Operation (σ)
It selects tuples that satisfy the given predicate from a relation.
Projection(π): It is used to project required column data from a
relation. Example: Consider Table 1. Suppose we want columns B and C
from Relation R.
π(B,C)R will show following columns.
AND NORMAL FORM
RELATIONAL MODEL
The relational model represents the database as a collection of relations. A relation is
nothing but a table of values. Every row in the table represents a collection of related data
values. These rows in the table denote a real-world entity or relationship. The table name
and column names are helpful to interpret the meaning of values in each row. The data are
represented as a set of relations. In the relational model, data are stored as tables.
However, the physical storage of the data is independent of the way the data are logically
organized.
Some popular Relational Database management systems are:
• DB2 and Informix Dynamic Server - IBM
• Oracle and RDB – Oracle
• SQL Server and Access - Microsoft
RELATIONAL MODEL CONCEPTS
1. Attribute: Each column in a Table. Attributes are the properties which define a
relation. e.g., Student_Rollno, NAME,etc.
2. Tables – In the Relational model the, relations are saved in the table format. It is stored
along with its entities. A table has two properties rows and columns. Rows represent
records and columns
represent attributes.
3. Tuple – It is nothing but a single row of a table, which contains a single record.
4. Relation Schema: A relation schema represents the name of the relation with its attributes.
5. Degree: The total number of attributes which in the relation is called the degree of the relation.
6. Cardinality: Total number of rows present in the Table.
7. Column: The column represents the set of values for a specific attribute.
8. Relation instance – Relation instance is a finite set of tuples in the RDBMS
system.Relation instances never have duplicate tuples.
9. Relation key - Every row has one, two or multiple attributes, which is called relation key.
10. Attribute domain – Every attribute has some pre-defined value and scope
which is known as attribute domain.
,Relational Integrity constraints
Relational Integrity constraints is referred to conditions which must be present
for a valid relation. These integrity constraints are derived from the rules in the
mini-world that the database represents.
There are many types of integrity constraints. Constraints on the Relational
database management system is mostly divided into three main categories are:
1. Domain constraints
2. Key constraints
3. Referential integrity constraints
DOMAIN CONSTRAINTS
Domain constraints can be violated if an attribute value is not appearing in the
corresponding domain or it is not of the appropriate data type.
Domain constraints specify that within each tuple, and the value of each attribute
must be unique. This is specified as data types which include standard data types
integers, real numbers, characters, Booleans, variable length strings, etc.
KEY CONSTRAINTS
An attribute that can uniquely identify a tuple in a relation is called the key of the
table. The value of the attribute for different tuples in the relation has to be unique.
REFERENTIAL INTEGRITY CONSTRAINTS
Referential integrity constraints is based on the concept of Foreign Keys. A foreign
key is an important attribute of a relation which should be referred to in other
relationships.
RELATIONAL OPERATIONS
A relational operation involves manipulating one or more tables, or relations , to result in
another table.
Relational Algebra is a procedural query language. Relational algebra mainly provides a
theoretical foundation for relational databases and SQL. The main purpose of using
Relational Algebra is to define operators that transform one or more input relations into an
output relation. Given that these operators accept relations as input and produce relations
as output, they can be combined and used to express potentially complex queries that
transform potentially many input relations (whose data are stored in the database) into a
single output relation (the query results). As it is pure mathematics, there is no use of
English Keywords in Relational Algebra and operators are represented using symbols.
Fundamental Operators
Thes basic/fundamental operators used in Relational Algebra.
Selection(σ)
Projection(π)
Union(U)
Set Difference(-)
Set Intersection(∩)
Rename(ρ)
Cartesian Product(X)
, Selection(σ): It is used to select required tuples of the
relations. Example:
For the above relation, σ(c>3)R will select the tuples which have c more than 3.
Note: The selection operator only selects the required tuples but does not display them. For
display, the data projection operator is used.
Select Operation (σ)
It selects tuples that satisfy the given predicate from a relation.
Projection(π): It is used to project required column data from a
relation. Example: Consider Table 1. Suppose we want columns B and C
from Relation R.
π(B,C)R will show following columns.
