Fast Identification of Relational Constraint Violations

Logical constraints, (e.g., `phone numbers in Toronto can have prefixes 416, 647, 905 only´), are ubiquitous in relational databases. Traditional integrity constraints, such as functional dependencies, are examples of such logical constraints as well. However, under frequent database updates, schema evolution and transformations, they can be easily violated. As a result, tables become inconsistent and data quality is degraded. In this paper we study the problem of validating collections of user defined constraints on a number of relational tables. Our primary goal is to quickly identify which tables violate such constraints. Logical constraints are potentially complex logical formuli, and we demonstrate that they cannot be efficiently evaluated by SQL queries. In order to enable fast identification of constraint violations, we propose to build and maintain specialized logical indices on the relational tables. We choose Boolean Decision Diagrams (BDD) as the index structure to aid in this task. We first propose efficient algorithms to construct and maintain such indices in a space efficient manner. We then describe a set of query re-write rules that aid in the efficient utilization of logical indices during constraint validation. We have implemented our approach on top of a relational database and tested our techniques using large collections of real and synthetic data sets. Our results indicate that utilizing our techniques in conjunction with logical indices during constraint validation offers very significant performance advantages.