Rename (relational algebra)
Encyclopedia
In relational algebra
, a rename is a unary operation
written as
where:
The result is identical to
except that the 
field in all tuple
s is renamed to an
field. For an example, consider the following 
relation and its renamed version:
|-
!
!
|- style="vertical-align: top"
|
{| align="center" border="0" cellpadding="5" cellspacing="0" style="border-collapse: collapse; border: 1px solid black"
|- style="background-color: silver; text-align: left"
! style="border: 1px solid black" | Name
! style="border: 1px solid black" | EmployeeId
|-
| style="border: 1px solid black" | Harry
| style="border: 1px solid black" | 3415
|-
| style="border: 1px solid black" | Sally
| style="border: 1px solid black" | 2241
|}
|
{| align="center" border="0" cellpadding="5" cellspacing="0" style="border-collapse: collapse; border: 1px solid black"
|- style="background-color: silver; text-align: left"
! style="border: 1px solid black" | EmployeeName
! style="border: 1px solid black" | EmployeeId
|-
| style="border: 1px solid black" | Harry
| style="border: 1px solid black" | 3415
|-
| style="border: 1px solid black" | Sally
| style="border: 1px solid black" | 2241
|}>
Formally the semantics of the rename operator is defined as follows:
where
is defined as the tuple 
with the 
attribute renamed to 
so that:
The result of the rename is only defined when the attribute
did not appear already in the
header
of the operand.
Relational algebra
Relational algebra, an offshoot of first-order logic , deals with a set of finitary relations that is closed under certain operators. These operators operate on one or more relations to yield a relation...
, a rename is a unary operation
Unary operation
In mathematics, a unary operation is an operation with only one operand, i.e. a single input. Specifically, it is a functionf:\ A\to Awhere A is a set. In this case f is called a unary operation on A....
written as
where:-
and 
are attributePropertyProperty is any physical or intangible entity that is owned by a person or jointly by a group of people or a legal entity like a corporation...
names -
is a relationRelation (mathematics)In set theory and logic, a relation is a property that assigns truth values to k-tuples of individuals. Typically, the property describes a possible connection between the components of a k-tuple...
The result is identical to
except that the field in all tupleTuple
In mathematics and computer science, a tuple is an ordered list of elements. In set theory, an n-tuple is a sequence of n elements, where n is a positive integer. There is also one 0-tuple, an empty sequence. An n-tuple is defined inductively using the construction of an ordered pair...
s is renamed to an
field. For an example, consider the following relation and its renamed version:!
!
|- style="vertical-align: top"
|
{| align="center" border="0" cellpadding="5" cellspacing="0" style="border-collapse: collapse; border: 1px solid black"
|- style="background-color: silver; text-align: left"
! style="border: 1px solid black" | Name
! style="border: 1px solid black" | EmployeeId
|-
| style="border: 1px solid black" | Harry
| style="border: 1px solid black" | 3415
|-
| style="border: 1px solid black" | Sally
| style="border: 1px solid black" | 2241
|}
|
{| align="center" border="0" cellpadding="5" cellspacing="0" style="border-collapse: collapse; border: 1px solid black"
|- style="background-color: silver; text-align: left"
! style="border: 1px solid black" | EmployeeName
! style="border: 1px solid black" | EmployeeId
|-
| style="border: 1px solid black" | Harry
| style="border: 1px solid black" | 3415
|-
| style="border: 1px solid black" | Sally
| style="border: 1px solid black" | 2241
|}>
Formally the semantics of the rename operator is defined as follows:
where
is defined as the tuple with the attribute renamed to so that:
The result of the rename is only defined when the attribute
did not appear already in theheader
Header
Header may refer to: Computers and engineering* Header , supplemental data at the beginning of a data block** E-mail header** HTTP header* Header file, a text file used in computer programming...
of the operand.