Although XQuery is a statically typed, functional query language for XML data, some of its features such as upward and horizontal XPath axes are typed imprecisely. The main reason is that while the XQuery data model allows us to navigate upwards and between siblings from a given XML node, the type model, e.g., regular tree types, can describe only the subtree structure of the given node. To alleviate this limitation, precise forward type inference systems for XQuery were recently proposed using an extended regular type language that can describe not only a given XML node but also its context. In this paper, as a different approach, we propose a novel backward type inference system for XQuery, based on a type language extended with logical formulas. Our backward type inference system provides an exact typing result for XPath axes and a sound typing result for XQuery expressions.

尽管XQuery是用于XML数据的静态类型的功能查询语言，但是其某些功能（例如，向上和水平XPath轴）的键入不精确。主要原因是，虽然XQuery数据模型允许我们在给定XML节点的同级之间向上导航，但类型模型（例如，，常规树类型，只能描述给定节点的子树结构。为了减轻这种限制，最近提出了一种使用扩展的常规类型语言的XQuery的精确正向类型推断系统，该语言不仅可以描述给定的XML节点，而且可以描述其上下文。在本文中，作为一种不同的方法，我们基于基于逻辑公式扩展的类型语言，提出了一种新颖的XQuery向后类型推理系统。我们的向后类型推断系统为XPath轴提供了准确的输入结果，为XQuery表达式提供了声音的输入结果。