Formal Definitions

1. An expression is of the form

   

   where the represent domain variables, and is a formula.

2. An atom in the domain relational calculus is of the following forms
   • where is a relation on attributes, and , are domain variables or constants.
   • , where and are domain variables, and is a comparison operator.

   • , where c is a constant.
3. Formulae are built up from atoms using the following rules:
   • An atom is a formula.
   • If is a formula, then so are and .

   • If and are formulae, then so are , and .
   • If is a formula where x is a domain variable, then so are and .