摘要
Mermaid is a testbed system which provides integrated access to multiple databases. We have developed two query optimization algorithms for Mermaid. The semijoin algorithm tends to reduce the data transmission cost while the replicate algorithm reduces the processing cost. In this paper, we present an algorithm which integrates the features of these two algorithms to optimize the processing cost as well as the transmission cost. Particularly, we consider a dynamic network environment where processing speeds at each site and transmission speeds at each link can be variable. Moreover, distributed processing of aggregates is considered based on the functional dependency among the fragment attribute, the aggregate attribute, and the group-by attribute. We also apply semantic information for efficient query processing. © 1989 IEEE