Three-Valued Logic

Acronym: 3VL

A logic system prevalent within SQL-based Database Management Systems (DBMSs) that is defined using three values, TRUE, FALSE, and UNKNOWN, as opposed to traditional boolean-valued logic systems that involve only two values, TRUE and FALSE. The system is used as a mechanism for reasoning in the presence of missing information. Within CQL, the three values are represented by the language keywords true, false, and null.