Query formulation is increasingly performed by systems that need to guess a user's intent (e.g. via spoken word interfaces). But how can a user know that the computational agent is returning answers to the "right" query? More generally, given that relational queries can become pretty complicated, how can we help users understand existing relational queries, whether human-generated or automatically generated? Now seems the right moment to revisit a topic that predates the birth of the relational model: developing visual metaphors that help users understand relational queries. This lecture-style tutorial surveys the key visual metaphors developed for visual representations of relational expressions. We will survey the history and state-of-the art of relationally-complete diagrammatic representations of relational queries, discuss the key visual metaphors developed in over a century of investigating diagrammatic languages, and organize the landscape by mapping their used visual alphabets to the syntax and semantics of Relational Algebra (RA) and Relational Calculus (RC).

翻译：查询制定日益由需要猜测用户意图的系统执行（例如通过语音界面）。但用户如何知道计算代理是否返回的是"正确"查询的答案？更一般地说，由于关系查询可能变得相当复杂，我们如何帮助用户理解现有的关系查询——无论是人工生成的还是自动生成的？现在似乎是重新审视一个早于关系模型诞生的话题的合适时机：开发帮助用户理解关系查询的可视化隐喻。本讲座式教程概述了为关系表达式的可视化表示而开发的关键可视化隐喻。我们将回顾关系完备的关系查询图解表示的历史和最新进展，讨论在一个多世纪的图解语言研究中开发的关键可视化隐喻，并通过将其使用的视觉字母表映射到关系代数和关系演算的语法和语义来组织这一领域的图景。