Then, this paper deeply investigated the three difficult problems of the system, such as exception handling, security right controlling and heterogeneous database access. 然後，就系統(tǒng)的三個(gè)難點(diǎn)問題——異常処理、安全權(quán)限控制和異搆數(shù)據(jù)庫訪問進(jìn)行了深入的研究。