论文标题

可直接访问联合查询的排名答案的可行订单

Tractable Orders for Direct Access to Ranked Answers of Conjunctive Queries

论文作者

Carmeli, Nofar, Tziavelis, Nikolaos, Gatterbauer, Wolfgang, Kimelfeld, Benny, Riedewald, Mirek

论文摘要

我们研究了何时可以根据指定的订单直接访问k-th答案(CQ),该订单是按时间对数的答案,以数据库的大小为对数的答案,然后按照预处理步骤在数据库大小中构建数据结构的预处理步骤。具体来说,我们面临着确定可进行的答案顺序的挑战,即允许这种复杂性保证的订单。为了更好地理解手头的计算挑战,我们还研究了仅提供单个答案的访问(即在给定位置找到答案)的更为适中的任务,我们将任务称为选择问题,并询问何时可以在准线性时间内执行。我们还探讨了何时选择比排名直接访问更容易的问题。 我们从词典订单开始。对于这两个问题中的每个问题,我们给出了无自结合的每个CQ的可拖动词典订单类别的可决定性表征(在常规复杂性假设下)。然后,我们继续通过属性权重的总和继续达到更一般的秩序,并为两个问题中的每个问题中的每个问题建立了相应的可决定性特征,而无需自加入。最后,我们探讨了何时将功能依赖性(FD)满意的问题用于拖延性,并为每组Unary FDS建立相应的表征概括。

We study the question of when we can provide direct access to the k-th answer to a Conjunctive Query (CQ) according to a specified order over the answers in time logarithmic in the size of the database, following a preprocessing step that constructs a data structure in time quasilinear in database size. Specifically, we embark on the challenge of identifying the tractable answer orderings, that is, those orders that allow for such complexity guarantees. To better understand the computational challenge at hand, we also investigate the more modest task of providing access to only a single answer (i.e., finding the answer at a given position), a task that we refer to as the selection problem, and ask when it can be performed in quasilinear time. We also explore the question of when selection is indeed easier than ranked direct access. We begin with lexicographic orders. For each of the two problems, we give a decidable characterization (under conventional complexity assumptions) of the class of tractable lexicographic orders for every CQ without self-joins. We then continue to the more general orders by the sum of attribute weights and establish the corresponding decidable characterizations, for each of the two problems, of the tractable CQs without self-joins. Finally, we explore the question of when the satisfaction of Functional Dependencies (FDs) can be utilized for tractability, and establish the corresponding generalizations of our characterizations for every set of unary FDs.

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