User errors in database query composition

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This research reports on the experimental test of several causes of user errors while composing database queries. The query language under consideration is Structured Query Language (SQL), the industry standard language for querying databases. Unfortunately, users commit many errors when using SQL. To understand user errors, a model of query writing was developed that integrated a GOMS-type analysis of query writing with the characteristics of human cognition. This model revealed multiple cognitive causes of a frequent and troublesome error, join clause omission. This semantic user error returns answers from the database that may be undetectably wrong, affecting users, decision makers, and programmers.The model predicted four possible causes of join clause omission, and empirical testing revealed that all four contributed to the error. Specifically, the frequency of this error increased because (1) the load on working memory caused by writing intervening clauses made the users forget to include the join clause, (2) an explicit clue to write the join clause was absent from the problem statement, (3) users inappropriately reused the procedure appropriate for a single table query, which requires no join clause, when a join clause is indeed necessary, and (4) some users never learned the correct procedure. These results are significant for understanding user errors in general and for developing new interfaces and training schemes for the task of writing database queries.