Logical operators (AND, OR, NOT, XOR)

Logical operators create properties that consider their operands as logical values of class BOOLEAN and whose return value is also a value of class BOOLEAN. If the value of an operand of a logical operator is not NULL, then the operand is treated as the value TRUE of class BOOLEAN, otherwise as NULL. The result is always either TRUE or NULL, never FALSE.

The platform currently supports the following logical operators:

Operator	Name	Description	Example	Result
AND	Conjunction	Takes two operands and returns TRUE if both operands are non-NULL	TRUE AND TRUE	TRUE
OR	Disjunction	Takes two operands and returns TRUE if either operand is non-NULL	NULL OR TRUE	TRUE
NOT	Negation	Takes one operand and returns TRUE if the operand is NULL	NOT TRUE	NULL
XOR	Exception	Takes two operands and returns TRUE if exactly one operand is non-NULL	TRUE XOR TRUE	NULL

With more than two operands, XOR returns TRUE when an odd number of operands are non-NULL.

Language

Description of logical operator syntax.

Examples

likes = DATA BOOLEAN (Person, Person);
likes(Person a, Person b, Person c) = likes(a, b) AND likes(a, c);
outOfInterval1(value, left, right) = value < left OR value > right;
outOfInterval2(value, left, right) = NOT (value >= left AND value <= right);