FLEX: A Tolerant and Cooperative User Interface to Databases

FLEX is a user interface to relational databases that can be used satisfactorily by users with different levels of expertise. FLEX is based on a formal query language, but is tolerant of incorrect input. It never rejects queries; instead, it adapts flexibly and transparently to their level of correctness and well-formedness, providing interpretations of corresponding accuracy and specificity. The most prominent design feature of FLEX is the smooth concatenation of several independent mechanisms, each capable of handling input of decreasing level of correctness and well-formedness. Each input is “cascaded” through this series of mechanisms, until an interpretation is found. FLEX is also cooperutive. It never delivers empty answers without explanation or assistance. By following up each failed query with a set of more general queries, FLEX determines whether an empty answer is genuine (it then suggests related queries that have nonempty answers), or whether it reflects erroneous presuppositions on behalf of the user (it then explains them).