Complex conditions

Function

A complex condition consists of a combination of two or more simple conditions.

Format

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condition {AND | OR} [NOT] condition  [{AND | OR} [NOT] condition] ...

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Syntax rules

1. condition specifies a simple condition.

2. Parentheses may be used within a complex condition to improve readability or to modify the normal hierarchical sequence of execution.

3. The simple conditions within a complex condition are separated from each other by logical operators, according to the specified rules. The logical operators must be preceded by a space and followed by a space.

4. A complex condition may comprise up to 60 simple conditions.

5. Table 22 lists the logical operators and their meanings.

   Operator	Meaning	Example
   OR	Logical inclusive Or (either or both)	The expression A OR B is true if A is true, or B is true, or both A and B are true.
   AND	Logical conjunction (both)	The expression A AND B is true only if both A and B are true.
   NOT	Logical negation	The expression "NOT" A is true only if A is false.

   Table 22: Logical operators

6. The ways in which conditions and logical operators may be combined are shown in Table 23.

   First symbol	Second symbol
   	simple-condition	OR	AND	NOT	(	)
   simple-condition	-	P	P	-	-	P
   OR	P	-	-	P	P	-
   AND	P	-	-	P	P	-
   NOT	P	-	-	-	P	-
   (	P	-	-	P	P	-
   )	-	P	P	-	-	P

   Table 23: Valid symbol pairs of conditions and logical operators¹

   ¹⁾ P indicates that the two symbols may be used as a pair.

7. Rules of precedence for evaluation of expressions

   The evaluation of complex conditions starts with the innermost pair of parentheses and proceeds through to the outermost pair of parentheses.

   If the order of evaluation is not determined by parentheses, the expression is evaluated according to the following precedence (hierarchical levels):

   • Arithmetic expressions

   • Relational operators

   • NOT conditions

   • AND and its associated conditions are evaluated from left to right.

   • OR and its associated conditions are evaluated last, also proceeding from left to right.

   • If consecutive expressions have the same hierarchical level, they are evaluated from left to right.

   Example 8-9

   Consider this expression:

   A IS NOT GREATER THAN B OR A + B IS EQUAL TO C AND D IS POSITIVE

   This expression is evaluated as if the following parentheses had been supplied:

   (A IS NOT GREATER THAN B) OR (((A+B) IS EQUAL TO C) AND (D IS POSITIVE)).

   Example 8-10

   Table 24 shows some of the relationships between logical operators and simple conditions.

   Operands	Value of A 1)	True	False	True	False
   	Value of B 1)	True	True	False	False
   Combinations	NOT A	False	True	False	True
   	A AND B	True	False	False	False
   	A OR B	True	True	True	False
   	NOT (A AND B)	False	True	True	True
   	NOT A AND B	False	True	False	False
   	NOT (A OR B)	False	False	False	True
   	NOT A OR B	True	True	False	True

   
   Table 24: Results of logical operators

   ¹⁾ A and B represent simple conditions.