Query Optimization in Heterogeneous Environment

目前，用户在检索存储在不同类型数据库系统中的信息时遇到困难。大多数用户不熟悉不同的查询语言，可能不知道数据的位置。这个项目的目标是促进异构数据库环境中的查询表述和加速查询处理，即不同类型的数据库系统，特别是关系、面向对象、演绎和文本系统共存于一个组织或跨不同组织的情况。为了使只熟悉一种查询语言的用户能够访问存储在不同类型数据库系统中的信息，正在构建查询语言的翻译器。构建智能数据字典，方便模式集成和查询转换。查询处理性能通过应用基于逻辑的方法来优化，这些方法使用了关于先前处理的查询类型的知识。采用跨不同系统的并行处理技术来提供进一步的加速。随着不同数据库系统联网的广泛应用，异构查询处理系统将具有广泛的适用性。

Currently, users have difficulties in retrieving information which is stored in different types of database systems. Most users are not familiar with different query languages and may not be aware of the locations of data. The objective of this project is to facilitate query formulation and to speed up query processing in heterogeneous database environments, i.e. where different types of database systems, specifically, relational, object-oriented, deductive, and textual systems co-exist in an organization or across different organizations. To enable a user who is familiar with only a single query language to access information stored in different types of database systems, translators of query languages are being built. An intelligent data dictionary is constructed to facilitate schema integration and query translation. Query processing performance is optimized by application of logic-based methods, using knowledge about the types of queries previously processed. Parallel processing techniques across different systems are employed to provide further speedup. The resulting heterogeneous query processing system will find wide applicability as the networking of different database systems becomes widespread.