SHACL is a W3C-proposed schema language for expressing structural constraints on RDF graphs. Recent work on formalizing this language has revealed a striking relationship to description logics. SHACL expressions can use three fundamental features that are not so common in description logics. These features are equality tests; disjointness tests; and closure constraints. Moreover, SHACL is peculiar in allowing only a restricted form of expressions (so-called targets) on the left-hand side of inclusion constraints. The goal of this paper is to obtain a clear picture of the impact and expressiveness of these features and restrictions. We show that each of the four features is primitive: using the feature, one can express boolean queries that are not expressible without using the feature. We also show that the restriction that SHACL imposes on allowed targets is inessential, as long as closure constraints are not used. In addition, we show that enriching SHACL with "full" versions of equality tests, or disjointness tests, results in a strictly more powerful language.

翻译：SHACL 是W3C提出的用于表达RDF图结构约束的模式语言。近期对该语言的形式化工作揭示其与描述逻辑存在惊人关联。SHACL表达式可使用三个在描述逻辑中不常见的核心特性：相等性测试、不相交性测试以及闭包约束。此外，SHACL的特殊之处在于其仅允许在包含约束左侧使用受限形式的表达式（即所谓的“目标”）。本文旨在系统阐明这些特性与限制的影响及表达能力。我们证明四个特性均具有原始性：使用任一特性可表达在不使用该特性时无法表达的布尔查询。同时证明当不使用闭包约束时，SHACL对允许目标的限制实质上是非本质的。此外，我们表明向SHACL引入相等性测试或不相交性测试的“完全”版本将产生严格更强的语言。