Abstract: The theory of conditional functional dependencies was introduced and its application for improving data quality was discussed. Firstly, conditional functional dependencies (CFDs) were defined and a set of sound and complete inference rules for CFDs were proposed; and dependency propagation was studied to find CFDs holding on views. Secondly, the consistency and implication problems for CFDs were analyzed. Then SQI. techniques were proposed to detect data inconsistency in relational database. Finally, extensions of CFDs were discussed.

Key words: Data quality, Data cleaning, Conditional functional dependencies, Inference rule, Dependency propagation,Consistency,Implication