Outerjoin is one of the most frequently used operators for integrating semantically related entity types in a multidatabase environment. Efficient view maintenance involving outerjoin is a challenging problem. Unfortunately, most of the existing view maintenance algorithms only consider the views defined by select-project-join (known as SPJ) queries. Once outerjoin is used as the integration operator to create a view, those existing algorithms may fail in view maintenance. In this paper, we first expose an abnormal phenomenon (we called it dangling tuple problem) of view maintenance when outer-join and data inconsistency are involved. We then propose a new view maintenance mechanism that can handle views involving outerjoin, regular join, and data inconsistency. It can also handle maintenance anomaly. Moreover, our maintenance mechanism minimizes the number of the queries that need to be sent to the local database systems for view maintennace, which is an effective way to make the multidatabase system more efficient.
展开▼
