分布式自治数据源的联合查询

不同数据源之间数据结构和表示方法的不同以及这些数据源在查询能力上受到的限制，使得对分布式异构数据源的集成和综合查询成为一个困难的问题、基于元数据描述，在语义正确的前提下，根据不同查询条件和不同数据源能力，自动构造查询计划是解决这个问题的一个可行方向，并可以根据实际需要有不同的具体方法，以快速构造查询计划为目的的直观算法，和以充分利用各种数据源尽可能全面构造所有可能的查询计划为目的的闭包算法是其中两种典型的方法，实验表明这两种方法具有不同的特点和适用情况。

Integration and Query of Diverse Data Sources

With the rapid development of Internet and WWW, integration of distributed and diverse data sources becomes a more and more important issue However, it is a difficult problem due to heterogeneous data structure and capabilities of these data sources One possible solution is to construct query plans according to the data source capabilities which are described as metadata A variety of methods serve this purpose due to different application requirements, two typical methods are studied here, one tries to construct simple but efficient query plan as quickly as possible, the other aims on getting as many semantically correct query answers as possible by exploiting semantic relationships among data sources These semantic relationships are expressed as mappings between the logical data space and each concrete data source Experiments are carried out to analyze and demonstrate the efficiency and effectiveness of these methods In the same time, complicated query conditions are also considered in order to assign appropriate query condition to each data source