Existential rule languages are a family of ontology languages that have been widely used in ontology-mediated query answering (OMQA). However, for most of them, the expressive power of representing domain knowledge for OMQA, known as the program expressive power, is not well-understood yet. In this paper, we establish a number of novel characterizations for the program expressive power of several important existential rule languages, including tuple-generating dependencies (TGDs), linear TGDs, as well as disjunctive TGDs. The characterizations employ natural model-theoretic properties, and automata-theoretic properties sometimes, which thus provide powerful tools for identifying the definability of domain knowledge for OMQA in these languages.

翻译：存在规则语言是本体学语言的大家庭,在以本体学为媒介的问答中广泛使用,然而,对大多数本体学语言来说,为OMQA(称为方案表达力)代表域知识的表达力尚不十分清楚,在本文件中,我们为几种重要的生存规则语言,包括产生图腾的依赖物(TGDs)、线性TGDs以及脱钩的TGDs等方案表达力建立了若干新特征,这些特征利用自然模型理论特性,有时还利用自制数据理论特性,从而提供了确定OMQA在这些语文中域知识可定义性的有力工具。