The problem of querying RDF data is a central issue for the development of the Semantic Web. The query language SPARQL has become the standard language for querying RDF since its W3C standardization in 2008. However, the 2008 version of this language missed some important functionalities: reasoning capabilities to deal with RDFS and OWL vocabularies, navigational capabilities to exploit the graph structure of RDF data, and a general form of recursion much needed to express some natural queries. To overcome these limitations, a new version of SPARQL, called SPARQL 1.1, was released in 2013, which includes entailment regimes for RDFS and OWL vocabularies, and a mechanism to express navigation patterns through regular expressions. Unfortunately, there are a number of useful navigation patterns that cannot be expressed in SPARQL 1.1, and the language lacks a general mechanism to express recursive queries. To the best of our knowledge, no efficient RDF query language that combines the above functionalities is known. It is the aim of this work to fill this gap. To this end, we focus on a core fragment of the OWL 2 QL profile of OWL 2 and show that every SPARQL query enriched with the above features can be naturally translated into a query expressed in a language that is based on an extension of Datalog, which allows for value invention and stratified negation. However, the query evaluation problem for this language is highly intractable, which is not surprising since it is expressive enough to encode some inherently hard queries. We identify a natural fragment of it, and we show it to be tractable and powerful enough to define SPARQL queries enhanced with the desired functionalities.

中文翻译：

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用于查询语义网的表达语言

查询RDF数据的问题是语义网发展的核心问题。自 2008 年 W3C 标准化以来，查询语言 SPARQL 已成为查询 RDF 的标准语言。然而，该语言的 2008 版本缺少一些重要功能：处理 RDFS 和 OWL 词汇表的推理能力，利用图结构的导航能力。 RDF 数据，以及表达一些自然查询非常需要的通用递归形式。为了克服这些限制，2013 年发布了一个新版本的 SPARQL，称为 SPARQL 1.1，其中包括 RDFS 和 OWL 词汇表的蕴涵机制，以及通过正则表达式表达导航模式的机制。不幸的是，有许多有用的导航模式无法在 SPARQL 1.1 中表达，并且该语言缺乏表达递归查询的通用机制。据我们所知，目前还没有结合上述功能的有效 RDF 查询语言。这项工作的目的是填补这一空白。为此，我们专注于 OWL 2 的 OWL 2 QL 配置文件的核心片段，并表明每个具有上述特性的 SPARQL 查询都可以自然地翻译成以基于 Datalog 扩展的语言表达的查询，这允许价值发明和分层否定。然而，这种语言的查询评估问题非常棘手，这并不奇怪，因为它的表达能力足以编码一些固有的困难查询。我们识别出它的一个自然片段，