1. An expression is of the form

{(x1,x2,...,xn)| P(x1, x2,...,xn)}

where the xi,1≤i ≤ n, represent domain variables, and P is a formula.

2. An atom in the domain relational calculus is of the following forms

• (x1, . . ., xn) 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.

3. Formulae are built up from atoms using the following rules:

• An atom is a formula.
• If P is a formula, then so are ï¿¢P and (P).
• If P1 and P2 are formulae, then so are P1 ∨ P2, P1 ∧ P2 and P1 ) P2.
• If P(x) is a formula where x is a domain variable, then so are Еx(P(x)) and x(P(x)).