arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 0712.1996cs.LOcs.CCcs.DB
收藏

约束数据库中量词消去困难的实例研究:移动对象数据库中的不在场证明查询

A case study of the difficulty of quantifier elimination in constraint databases: the alibi query in moving object databases

Bart Kuijpers, Walied Othman, Rafael Grimson

摘要:

在约束数据库模型中,空间和时空数据通过实数上的多项式等式和不等式的布尔组合来存储。多项式约束扩充的关系演算是约束数据库的标准一阶查询语言。虽然这种查询语言的表达能力已被广泛研究,查询的有效评估的困难,通常涉及某种形式的量词消去,已收到相当少的关注。现有量词消除软件的效率低下和量词消去的固有困难已被证明是约束数据库系统实际实现的瓶颈。在本文中,我们专注于一个特定的查询,称为\emph{alibi query},询问是否两个移动的对象,其位置是已知的,在某些时刻的时间,可能会满足,给定一定的速度限制。这个查询可以被看作是一个约束数据库查询,它的求值依赖于消除一个由三个存在量词组成的块。通用消除算法的实现在特定情况下,出于实际目的,在回答不在场证明查询时太慢,并且在参数情况下完全失败。本文的主要贡献是参数不在场证明查询的一个解析解,它可以用来回答这个查询在特定的情况下,在常数时间。我们还给出了一个解析解的不在场证明查询在一个固定的时刻。我们提出的解决方案是基于几何论证,它们说明了这样一个事实,即一些实际问题需要创造性的解决方案,至少在理论上,现有的系统可以提供一个解决方案。

英文摘要:

In the constraint database model, spatial and spatio-temporal data are stored by boolean combinations of polynomial equalities and inequalities over the real numbers. The relational calculus augmented with polynomial constraints is the standard first-order query language for constraint databases. Although the expressive power of this query language has been studied extensively, the difficulty of the efficient evaluation of queries, usually involving some form of quantifier elimination, has received considerably less attention. The inefficiency of existing quantifier-elimination software and the intrinsic difficulty of quantifier elimination have proven to be a bottle-neck for for real-world implementations of constraint database systems. In this paper, we focus on a particular query, called the \emph{alibi query}, that asks whether two moving objects whose positions are known at certain moments in time, could have possibly met, given certain speed constraints. This query can be seen as a constraint database query and its evaluation relies on the elimination of a block of three existential quantifiers. Implementations of general purpose elimination algorithms are in the specific case, for practical purposes, too slow in answering the alibi query and fail completely in the parametric case. The main contribution of this paper is an analytical solution to the parametric alibi query, which can be used to answer this query in the specific case in constant time. We also give an analytic solution to the alibi query at a fixed moment in time. The solutions we propose are based on geometric argumentation and they illustrate the fact that some practical problems require creative solutions, where at least in theory, existing systems could provide a solution.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑