Tuple & Domain Relational Calculus In DBMS Explain With Examples

Relational Calculus Explain With Types, Tuple & Domain Relational Calculus In DBMS Explain With Examples

Relational calculus

It is a nonprocedural query language.
It describes the desired information without giving a specific procedure for obtaining that information.
Two types of relational calculus
Tuple relational calculus
Domain relational calculus

Tuple Relational Calculus

A nonprocedural query language, where each query is of the form
{t | P (t ) }
It is the set of all tuples t such that predicate or condition P is true for t.

Domain Relational Calculus

A form of Relational Calculus which uses domain variables that take on values from an attributes domain, rather than values for an entire tuple.
Definition:
An expression in Domain Calculus is of the form

{< x1, x2, … , xn > | P(x1, x2, … , xn) }
where
x1, x2, … , xn represents domain variables
P  represents a formula composed of atoms

An Atom has the form
< x1, x2, … , xn > ∈ r , where r is a relation on n attributes and x1, x2, … , xn are the domain variables or domain constraints.
xΘy , where x and y are domain variables and Θ is the comparison operator (<,>, ≤, ≥, =, ≠).  It is required that x and y have domains that can be compared by Θ.

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