RELATIONAL MODEL
Relational model is simple model in which database is represented as
a collection of “relations”
where each relation is represented by two-dimensional table.
The relational model was founded by E. F. Codd of the IBM in 1972.
The basic concept in the relational model is that of a relation.
Properties:
o It is column homogeneous. In other words, in any given column
of a table, all items are of the same kind.
o Each item is a simple number or a character string. That is a
table must be in first normal form.
o All rows of a table are distinct.
o The ordering of rows with in a table is immaterial.
o The column of a table are assigned distinct names and the
ordering of these columns is immaterial.
Domain, attributes tuples and relational:
Tuple:
Each row in a table represents a record and is called a tuple .A table
containing ‘n’ attributes in a
record is called is called n-tuple.
, Attributes:
The name of each column in a table is used to interpret its meaning
and is called an attribute. Each table is called a relation. In the above
table, account_number, branch name, balance are the attributes.
Domain:
A domain is a set of values that can be given to an attributes. So
every attribute in a table has a specific domain. Values to these
attributes cannot be assigned outside their domains.
Relation:
A relation consist of
o Relational schema
o Relation instance
Relational Schema:
A relational schema specifies the relation’s name, its attributes and the
domain of each attribute. If R is the name of a relation and A1,
A2,…An is a list of attributes representing R then R(A1,A2,…,An) is
called a Relational Schema. Each attribute in this relational schema
takes a value from some specific domain called domain(Ai).
Example:
PERSON (PERSON_ID:INTEGER, NAME:STRING, AGE:INTEGER,
ADDRESS:STRING)
Total number of attributes in a relation denotes the degree of a relation
since the PERSON relation scheme contains four attributes, so this
relation is of degree 4.
Relation Instance:
A relational instance denoted as r is a collection of tuples for a given
relational schema at a specific point of time.
A relation state r to the relations schema R(A1, A2…, An) also
Relational model is simple model in which database is represented as
a collection of “relations”
where each relation is represented by two-dimensional table.
The relational model was founded by E. F. Codd of the IBM in 1972.
The basic concept in the relational model is that of a relation.
Properties:
o It is column homogeneous. In other words, in any given column
of a table, all items are of the same kind.
o Each item is a simple number or a character string. That is a
table must be in first normal form.
o All rows of a table are distinct.
o The ordering of rows with in a table is immaterial.
o The column of a table are assigned distinct names and the
ordering of these columns is immaterial.
Domain, attributes tuples and relational:
Tuple:
Each row in a table represents a record and is called a tuple .A table
containing ‘n’ attributes in a
record is called is called n-tuple.
, Attributes:
The name of each column in a table is used to interpret its meaning
and is called an attribute. Each table is called a relation. In the above
table, account_number, branch name, balance are the attributes.
Domain:
A domain is a set of values that can be given to an attributes. So
every attribute in a table has a specific domain. Values to these
attributes cannot be assigned outside their domains.
Relation:
A relation consist of
o Relational schema
o Relation instance
Relational Schema:
A relational schema specifies the relation’s name, its attributes and the
domain of each attribute. If R is the name of a relation and A1,
A2,…An is a list of attributes representing R then R(A1,A2,…,An) is
called a Relational Schema. Each attribute in this relational schema
takes a value from some specific domain called domain(Ai).
Example:
PERSON (PERSON_ID:INTEGER, NAME:STRING, AGE:INTEGER,
ADDRESS:STRING)
Total number of attributes in a relation denotes the degree of a relation
since the PERSON relation scheme contains four attributes, so this
relation is of degree 4.
Relation Instance:
A relational instance denoted as r is a collection of tuples for a given
relational schema at a specific point of time.
A relation state r to the relations schema R(A1, A2…, An) also
