Abstract: To represent the logical difference of tuples and attribute values, a dual description logic for databases was introduced, in which concepts are classified into two classes; tuple concepts and attribute-value concepts. The logical language, syntax and semantics of the dual description logic for databases were introduced; two transformations from the relations in databases into knowledge bases or models in DDLD were defined; and finally an extended dual description logic for databases was introduced, in which roles are classified into three classes; the roles between tuples, the roles between tuples and attribute values and the roles between attribute values.

Key words: Description logic, Database, Concept, Role, Attribute