Dynamic Query Optimization and Query Processing in Multidatabase Systems.
Henryk Josiński · 2000
Introduction The multidatabase system (MDBS) approach, as a solution for integrated access to information distributed among diverse data sources, has gained a lot of attention in recent years. The multidatabase system is a database system which integrates pre--existing databases allowing the users to access simultaneously database systems (DBMSs) formulating a global query based on a global schema. The component DBMSs are assumed to be heterogeneous and autonomous. Heterogeneity refers to different user interfaces, data models, query languages, and query optimization strategies [5]. Local autonomy means that each DBMS retains complete control over local data and processing. As result of this, its cost model may not be available to the global query optimizer. When a global query is submitted, it is decomposed into two types of queries [1]: -- subqueries, operating on sharable data items from local databases, -- assembling queries, consisting of,