基于空值修复的数据库一致性查询方法*

完整性约束常用来定义数据库的数据语义，违反约束的数据库实例为不一致数据库，返回含有不一致结果的查询称为不一致查询。一致性查询目的在于不修改数据库实例而从不一致数据库获取满足约束的查询结果，已有方法因其支持的约束类型有限或计算复杂度高而影响其应用范围。提出了一种基于空值修复的数据库一致性查询方法，首先将原始完整性约束转换为与查询相关的统一约束，然后根据统一约束对原SQL查询进行查询重写，重写后的查询将不一致属性值当做空值来处理以获得满足完整性约束的结果。系统实现与实验证明，该方法在多种完整性约束类型与SQL

Consistent query answering based on virtual repairs with nulls

ntegrity constraints are used to define the data semantics in databases. The database instanced and the tuples violating the constraints were inconsistent. Consistent query answering was one technique to obtain consistent answer from inconsistent database. The applicable areas of current techniques were limited because they supported little types of constraints or their high computation complexity. This paper presented a new approach based on null repair. Transformed the constraints first to unified format to locate inconsistency, and then rewritten the original SQL queries to query consistent answers by treating inconsistent attributes as nulls. The implementation of the system and the experiment results show that this approach can achieve stable performance under multiple combinations of constraints and SQL queries.