2.7.5 Searching for data using a Boolean predicate

If the result of a function defined by an abstract data type or the result of a user-defined function is a Boolean value (TRUE, FALSE, or UNKNOWN), use a Boolean predicate for the true/false decision. For details about data retrieval strings that use a Boolean predicate, see 2.12.1 Abstract data types provided by the HiRDB Text Search Plug-in.