Improving The Human Factors Aspect Of Database Interactions. / quote 3 of 4
Problems with database query languages
Two problems come to mind with this yardstick in evaluating the human factors aspect of a language: (1) Many queries that can be written with a relationally complete language are extremely difficult to compose or comprehend. Few people claim to have a thorough understanding of first-order predicate calculus. (2) Many common, useful, simple to understand, and potentially easy to express queries are outside the bounds of relational completeness. For example, in a table of distances between adjacent cities, finding the shortest path between two remote cities is not included in relational completeness. Simi- larly, in a table of employees and their managers, finding the names of all the employees that a given individual manages at all levels, is not a relationally complete query.