Aggregate Queries Over Conditional Tables
Aggregate Queries Over Conditional Tables
复制标题
对条件表的聚合查询
DOI：
10.1023/a:1020197923385
复制
发表时间：
2002
影响因子：
3.4
通讯作者：
G. Vossen
中科院分区：
文献类型：
--
作者：
Jens Lechtenbörger;H. Shu;G. Vossen
条件表很久以前就被认为是捕获未知或不完整信息的一种方法。但是，对条件表的查询从来不允许涉及列函数，如聚合。本文将条件表理论向这个方向扩展，证明了存在一个强表示系统，它具有闭包性质，即条件表上的聚集查询结果可以再次由条件表表示。然而，事实证明，条件表中表示聚合查询结果的元组数量可能会随着表中变量的数量呈指数增长。对这一现象进行了详细的分析，给出了聚集查询结果中元组个数的严格上界和下界。最后，表示技术的草图，近似聚合结果在合理的大小表。
Conditional tables have been identified long ago as a way to capture unknown or incomplete information. However, queries over conditional tables have never been allowed to involve column functions such as aggregates. In this paper, the theory of conditional tables is extended in this direction, and it is shown that a strong representation system exists which has the closure property that the result of an aggregate query over a conditional table can be again represented by a conditional table. It turns out, however, that the number of tuples in a conditional table representing the result of an aggregate query may grow exponentially in the number of variables in the table. This phenomenon is analyzed in detail, and tight upper and lower bounds concerning the number of tuples contained in the result of an aggregate query are given. Finally, representation techniques are sketched that approximate aggregation results in tables of reasonable size.