RDF (Resource Description Framework) is a standard language to represent graph databases. Query languages for RDF databases usually include primitives to support path queries, linking pairs of vertices of the graph that are connected by a path of labels belonging to a given language. Languages such as SPARQL include support for paths defined by regular languages (by means of Regular Expressions). A context-free path query is a path query whose language can be defined by a context-free grammar. Context-free path queries can be used to implement queries such as the "same generation queries", that are not expressible by Regular Expressions. In this paper, we present a novel algorithm for context-free path query processing. We prove the correctness of our approach and show its run-time and memory complexity. We show the viability of our approach by means of a prototype implemented in Go. We run our prototype using the same cases of study as proposed in recent works, comparing our results with another, recently published algorithm. The experiments include both synthetic and real RDF databases. Our algorithm can be seen as a step forward, towards the implementation of more expressive query languages.

中文翻译：

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图数据库上的上下文无关路径查询算法

RDF（资源描述框架）是一种表示图形数据库的标准语言。RDF 数据库的查询语言通常包括支持路径查询的原语，链接图的顶点对，这些顶点对由属于给定语言的标签路径连接。SPARQL 等语言支持由正则语言（通过正则表达式）定义的路径。上下文无关路径查询是一种路径查询，其语言可以由上下文无关文法定义。上下文无关路径查询可用于实现诸如“同代查询”之类的查询，这些查询无法通过正则表达式表达。在本文中，我们提出了一种用于上下文无关路径查询处理的新算法。我们证明了我们方法的正确性，并展示了它的运行时间和内存复杂性。我们通过在 Go 中实现的原型展示了我们方法的可行性。我们使用最近工作中提出的相同研究案例运行我们的原型，将我们的结果与另一个最近发布的算法进行比较。实验包括合成和真实的 RDF 数据库。我们的算法可以看作是朝着实现更具表现力的查询语言迈出的一步。