DO2 is a deductive object-oriented database developed at the National University of Singapore. The system aims to integrate deductive and object-oriented paradigms and use their advantages to overcome both the paradigms’ respective weaknesses. DO2 differs from conventional deductive object-oriented databases in its' key-based approach for OIDs, pro-active approach to resolving inheritance conflicts and natural interpretation of negation using the not predicates. This paper describes the structure, language, and implementation of DO2.