完整性约束下数据库中数值型属性固定的复杂性与近似性
Complexity and Approximation of Fixing Numerical Attributes in Databases Under Integrity Constraints
摘要：
一致性查询应答是从数据库中计算答案的问题，这些答案相对于数据库作为一个整体可能无法满足的某些完整性约束是一致的。这些答案的特点是那些在最小形式的恢复数据库的一致性是不变的。在这种情况下，我们研究了修复数据库的问题，通过固定的整数数值在属性级拒绝和聚合约束。我们引入了一个定量的数据库修复的定义，并研究了几个决策和优化问题的复杂性，包括DFP，即存在的修复在一个给定的距离从原始实例，和CQA，即决定答案的一致性聚合合取查询下不同的语义。我们提供尖锐的复杂性界限，确定相关的易处理的情况下，并介绍近似算法的一些是棘手的。更具体地说，我们得到的结果，如不可判定的存在的修复聚合约束; MAXSNP硬度的DFP，但一个很好的近似算法的相关特殊情况下;和棘手的，但很好的近似CQA聚合查询一个数据库原子拒绝（加上内置的）。
英文摘要：
Consistent query answering is the problem of computing the answers from a database that are consistent with respect to certain integrity constraints that the database as a whole may fail to satisfy. Those answers are characterized as those that are invariant under minimal forms of restoring the consistency of the database. In this context, we study the problem of repairing databases by fixing integer numerical values at the attribute level with respect to denial and aggregation constraints. We introduce a quantitative definition of database fix, and investigate the complexity of several decision and optimization problems, including DFP, i.e. the existence of fixes within a given distance from the original instance, and CQA, i.e. deciding consistency of answers to aggregate conjunctive queries under different semantics. We provide sharp complexity bounds, identify relevant tractable cases; and introduce approximation algorithms for some of those that are intractable. More specifically, we obtain results like undecidability of existence of fixes for aggregation constraints; MAXSNP-hardness of DFP, but a good approximation algorithm for a relevant special case; and intractability but good approximation for CQA for aggregate queries for one database atom denials (plus built-ins).
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