Before revision:  However, since the knowledge in logical databases in practice always is incomplete  , forward reasoning of automated reasoning systems alone does not suffice to derive answers to questions because, instead of complete proofs, often only partial positive knowledge can be derived .
After revision:  However, since the knowledge in logical databases in practice always is incomplete . Hence , forward reasoning of automated reasoning systems alone does not suffice to derive answers to questions because, instead of complete proofs, often only partial positive knowledge can be derived .