Consistent Answers to SQL Queries

随着在线数据源中可用信息的爆炸式增长，人们越来越关注用户查询答案的一致性和质量。这个项目解决了使用逻辑完整性约束来衡量查询答案的一致性和质量的问题。尽管跨不同数据源强制执行全局完整性约束并通过更新单个数据源来纠正完整性违规是不切实际的，但完整性约束捕获了数据的重要语义属性。这个项目研究了数据库修复和一致查询答案的正式概念：在数据库的每次最小修复中都有一致的答案。关于答案一致性的信息是其质量和可靠性的重要标志。开发了在关系数据模型和SQL环境下计算一致性查询答案的各种程序，并分析了它们的计算复杂度。这些过程利用SQL的特定子集和完整性约束的特定类的属性。通过提供关于查询答案一致性的信息，这些过程将以一种非侵入性的方式增强现有DBMS的功能，特别是在数据集成应用程序的上下文中。

As the amount of information available in online data sources explodes, there is a growing concern about the consistency and quality of answers to user queries. This project addresses the issue of using logical integrity constraints to gauge the consistency and quality of query answers. Although it is impractical to enforce global integrity constraints across different data sources and correct integrity violations by updating individual sources, integrity constraints capture important semantic properties of data. This project studies the formal notions of database repair and consistent query answer: a consistent answer is true in every minimal repair of the database. The information about answer consistency serves as an important indication of its quality and reliability. A variety of procedures for computing consistent query answers in the context of the relational data model and SQL are developed, and their computational complexity analyzed. The procedures exploit the properties of specific subsets of SQL and specific classes of integrity constraints. By providing information about query answer consistency, such procedures will enhance the functionality of existing DBMS in a non-intrusive way, particularly in the context of data integration applications.