使用只读函数在概率数据库中快速查询
Faster Query Answering in Probabilistic Databases using Read-Once Functions
摘要：
如果布尔表达式的每个变量只出现一次，则该表达式为只读形式。当变量表示概率空间中的独立事件时，由只读形式的整个表达式表示的事件的概率可以在多项式时间内计算（而任意表达式的一般问题是#P-完全的）。检查只读属性的已知方法似乎需要将这些表达式置于析取范式中。在本文中，我们讲述了一个更好的故事布尔事件表达式的一个大的子类：那些没有自连接和元组独立的概率数据库上的合取查询生成的。我们首先表明，给定一个元组独立的表示和起源图的SPJ查询计划没有自连接，我们可以，而不使用DNF的结果事件表达式，有效地计算其同现图。由此，如果存在一次读取形式，则已经可以使用现有技术高效地计算该形式。我们的第二个和关键的贡献是一个完整的，高效的，简单的实现算法，直接计算只读一次的形式（只要它们存在），使用一个新的概念，即共表图，它可以显着小于同现图。
英文摘要：
A boolean expression is in read-once form if each of its variables appears exactly once. When the variables denote independent events in a probability space, the probability of the event denoted by the whole expression in read-once form can be computed in polynomial time (whereas the general problem for arbitrary expressions is #P-complete). Known approaches to checking read-once property seem to require putting these expressions in disjunctive normal form. In this paper, we tell a better story for a large subclass of boolean event expressions: those that are generated by conjunctive queries without self-joins and on tuple-independent probabilistic databases. We first show that given a tuple-independent representation and the provenance graph of an SPJ query plan without self-joins, we can, without using the DNF of a result event expression, efficiently compute its co-occurrence graph. From this, the read-once form can already, if it exists, be computed efficiently using existing techniques. Our second and key contribution is a complete, efficient, and simple to implement algorithm for computing the read-once forms (whenever they exist) directly, using a new concept, that of co-table graph, which can be significantly smaller than the co-occurrence graph.
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。
