异构数据源集成系统中基于数据源能力的查询分解和优化策略

异构数据源集成系统需要集成查询能力差别较大的各种数据源。为充分利用数据源的查询能力和简化包装器设计，本文提出使用复合法进行基于能力的查询分解和优化。在复合法中，仅需简单说明数据的基本查询能力，各数据源对查询处理的特殊限制封装在包装器中。文中给出描述数据源基本查询能力的方法，并且在讨论ＯＩＭ对象代数操作的概括查询和过滤子的基础上，探讨数据源包装器对基本支持查询的处理方法。

CAPABILITIES-BASED QUERY DECOMPOSITION AND OPTIMIZATION IN HETEROGENEOUS DATA INTEGRATION SYSTEM

A heterogeneous data integration system can integrate a broad range of data sources that provide different levels of query capabilities. Some data sources can only support simple scanning, such as file systems. Some data sources can support query using boolean expressions, such as text retrieval systems. Some data sources can even support complex operations such as joining in relational database systems.The declarative approach, which uses some languages to express query capabilities of various data sources, is difficult to describe some particular limits for query processing, while the encapsulation approach leads to very complex wrappers. To simplify the design of wrappers for data sources with limited capabilities, a kind of approach, named compound approach, which can take advantage of all powers of various data sources , is proposed for query decomposition and optimization. Different from the declarative approach and the encapsulation approach proposed formerly, the compound approach only needs brief declarations of basic query powers, but leaves the minute details of the capabilities and restrictions of the underlying data sources encapsulated in their wrappers. The concept of capability vector is proposed for describing basic query powers of data sources. Furthermore, with subsuming queries and filters of OIM algebra operations, the way for processing of queries basically supported in wrappers is given in this paper.