One of the most important functionalities of a database system is to answer queries. We are interested in the following question: If there exists more than one answer to the given query, which one should the database report? There are two apparent choices: to return all the valid answers or to return one of them. The problem with the former choice is that it is often time-prohibitive to search for all valid answers. In the latter choice, fairness may become an issue, since the index built for fast search may introduce bias to the query result. For example, the index may favor a certain portion of the input data (e.g., nodes near the root of a tree index) and with a higher chance, output an answer related to that portion than other portions. Such bias can sometimes lead to undesirable consequences.

中文翻译：

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技术视角

数据库系统最重要的功能之一是回答查询。我们对以下问题感兴趣：如果给定查询存在多个答案，数据库应该报告哪一个？有两种明显的选择：返回所有有效答案或返回其中一个。前一种选择的问题在于搜索所有有效答案通常是时间限制的。在后一种选择中，公平性可能会成为一个问题，因为为快速搜索而构建的索引可能会给查询结果带来偏差。例如，索引可能有利于输入数据的某个部分（例如，树索引根附近的节点），并且与其他部分相比，输出与该部分相关的答案的机会更高。这种偏见有时会导致不良后果。