Domain Relational Calculus

Domain Relational Calculus Domain variables take on values from an attribute’s domain, rather than values for an entire tuple. An expression is of the form: { | Q(x1, x2,…, xn)} Where the xi, 1≤ i ≤ ni represent domain variables, and Q is a formula. 1. An atom in the domain relational calculus is of the following forms: • € r where r is a relation on n attributes, and xi, 1 ≤ i ≤ n, are domain variables or constants. • x Θ y, where x and y are domain variables, and Θ is a comparison operator. • x Θ c, where c is a constant. 2. Formulae are built up from atoms using the following rules: • An atom is a formula. • If Q is a formula, then so are Q and (Q). • If Q1 and Q2 are formulae, then so are Q1 V Q2, Q1 Λ Q2 and Q1 => Q2. • If Q(x) is a formula where x is a domain variable, then so are x (Q(x)) and x(Q(x))