Abstract: The join dependency in database can bring about data redundancy, but in the actual database design and maintenance, it is not realistic to determine whether there is join dependency according to the definition of the concept. The data dependency reflects the realistic semantic constraints between different data’s items, belongs to the semantic areas. And finding the correct data dependency is also based on the semantic rules contained in data. This article discusses the general ideas and methods of finding the correct join dependency by some instances. The work has the theory reference value for the data mining and promoting data quality.

Key words: join dependency, semantic rule, data mining, data quality