Calling Boolean Functions

This section describes the Boolean functions that you can call in a query. The operations you can perform are

Converting an Object to Boolean

In some situations, you might want to force a Boolean comparison. The XPath processor performs a Boolean comparison if either operand is a Boolean value. Consequently, if neither operand is a Boolean value, call the boolean() function on one operand to convert it to a Boolean value. The XPath processor automatically converts the other operand to a Boolean value. The format of the boolean() function is

The boolean() function converts its argument to Boolean as follows:

The boolean() function is useful in comparisons. For example, the following query returns b elements that either contain both c and d elements as children or contain neither c nor d elements as children:

/a/b[boolean(c) = d]

To obtain the opposite Boolean value, call the not() function. The format is

boolean not(boolean) 

To obtain the value false, call the false() function. The format is

boolean false() 

Determining the Context Node Language

To determine whether the language of the context node is the language you expect it to be, call the lang() function. The format is

boolean lang(string) 

If there is no such attribute, then lang() returns false. If there is such an attribute, lang() returns true in the following situations:

In both situations, case is ignored. For example:

This returns true if the context node is any of these elements: