Over the past few years, we have seen the emergence of large knowledge graphs combining information from multiple sources. Sometimes, this information is provided in the form of assertions about other assertions, defining contexts where assertions are valid. A recent extension to RDF which admits statements over statements, called RDF-star, is in revision to become a W3C standard. However, there is no proposal for a semantics of these RDF-star statements nor a built-in facility to operate over them. In this paper, we propose a query language for epistemic RDF-star metadata based on a four-valued logic, called eSPARQL. Our proposed query language extends SPARQL-star, the query language for RDF-star, with a new type of FROM clause to facilitate operating with multiple and sometimes conflicting beliefs. We show that the proposed query language can express four use case queries, including the following features: (i) querying the belief of an individual, (ii) the aggregating of beliefs, (iii) querying who is conflicting with somebody, and (iv) beliefs about beliefs (i.e., nesting of beliefs).

本研究解决了RDF-star语义缺失及其操作工具不足的问题。提出了一种基于四值逻辑的查询语言eSPARQL，扩展了现有的SPARQL-star，使其能够处理多种相互冲突的信念。该语言能够有效表达个体信念查询、信念聚合及信念之间的冲突等功能，具有重要的实用价值。

eSPARQL：在RDF-star知识图谱中表示和调和不可知和无神论信仰