数据集成中XML数据查询语义重写

查询重写是数据库研究的一个基本问题，它和查询优化，数据仓库，数据集成，语义缓存等数据库问题密切相关，为提高集成系统的查询效率，系统选择提交频率较高的XML查询物化为中间层视图，用户提交查询后，系统尽可能利用中间视图层中视图，而不是访问数据源来回答查询，这个问题实际可以归结为半结构化查询重写问题，考虑到中间视图层空间的有限性，已有视图应当尽可能回答更多的查询，传统查询重写方法有考虑半结构化数据之间的约束，而根据约束可以等价变换查询，从而提高中间视图层中的表达能力，提出了一种新的半结构化查询重写的方法，该方法在保证算法正确性和完备性的基础上，利用上半结构化数据中的约束，尤其是XML文件中的路径依赖，来增强中间层物化视图的表达能力，理论分析和初步原型实验证明方法的有效性。

SEMANTIC QUERY REWRITING FOR XML DATA IN DATA INTEGRATION

Query rewriting is a basic problem in database research. It is relevant in many aspects of database management, including query optimization, datawarehouse, data integration, semantic cache etc. In order to improve the efficiency of integration system, the frequently submitted XML views are selected to materialize in mediator layer. After end users submit a query, the system tries to use views in mediator layer rather than the access to the data source to answer the query. Such a problem could be reduced to the semi-structured query rewriting. Due to the limited space in the mediator layer, the existing views should answer as more queries as possible. Traditional methods do not take into account the constraints in the semi-structured data, while the constraints play an important role in the transformation of queries hence enhancing the expressive ability of existing views. In this paper, a novel method is explored to make use of semantic constraints, especially path constraints in XML documents to enhance the expressive ability of materialized view in the mediator layer. The soundness and completeness of the algorithm are maintained. The theoretical analysis and prototype preliminary experiment results prove the validation of the method.