An experimental study of the interpretation of logical operators in database querying

The use of logical operators in query languages is considered to be a major source of user problems in database querying. The present study investigated whether people untrained in logic could succesfully interpret logical operators; and, how errors and latencies are related to the structure of the query. In an experiment, the logical complexity of an SQL-style query formulation was varied in using AND, OR, and NOT operators in either single or combined form. The latency and error data converged to show that subjects had increasingly difficulty with queries constructed with a combination of different operators. The inclusion of parentheses had a strong positive effect on task performance. Verbal protocols were used to identify sources of errors in query processing. A model of query processing was formulated and predictions of latencies and errors on the basis of processing components were tested.