Property graphs may be constrained by schemas that inform both query engines and human users about the shape of valid data, enforcing a contract between data provider and consumer. Composable property-graph queries transform input graphs into output graphs. Then, the question arises of which schema can be expected after one (or several) transformation steps. We investigate how schema constraints can be inferred given an input schema and a transforming query. Specifically, we propose a reasoning procedure that, given an input schema in ProGS and a query in G-CORE infers an output schema. Since graph updates will happen frequently, our inference procedure does not rely on graph instances, such that the computed output schema applies to all graphs originating from any input graph complying with the input schema. Related work has addressed this problem for SPARQL CONSTRUCT queries, encoding it in Description Logics (DLs) so that the output schema is entailed by axioms inferred from input schema and queries. Property graphs and their queries, however, complicate the matter, as property graphs feature label and property annotations as well as first-class edges. Thus, reification has to be used in one way or another, though available DLs lack the means to encode such features directly. We approach this novel challenge via a family of mappings for i) property graphs reified in RDF, aligned with ii) a mapping from ProGS to SHACL and iii) a mapping from G-CORE to SPARQL CONSTRUCT queries. In this manner, schema inference for property graphs becomes manageable, as we break apart the problem through the extra mapping layer and utilize efficient DL reasoners. We develop the metatheory regarding the soundness of inferred schema constraints and the semantic equivalence of mapped schemas and queries.

翻译：属性图可通过模式加以约束，这些模式既向查询引擎也向人类用户告知有效数据的形状，从而强化数据提供者与消费者之间的契约。可组合属性图查询将输入图转换为输出图。由此产生的问题是：在经历一次或多次转换步骤后，可以预期得到何种模式。我们研究了如何根据输入模式和转换查询来推断模式约束。具体而言，我们提出了一种推理过程：给定ProGS格式的输入模式和G-CORE格式的查询，该过程能够推断出输出模式。由于图更新将频繁发生，我们的推理过程不依赖于图实例，因此计算出的输出模式适用于所有源自任何符合输入模式的输入图的图。相关研究已针对SPARQL CONSTRUCT查询解决了此问题，方法是将问题编码到描述逻辑中，使得输出模式可从输入模式和查询推断出的公理中导出。然而，属性图及其查询使问题复杂化，因为属性图具有标签和属性注释以及一等公民的边。因此，无论如何都必须使用具体化机制，但现有的描述逻辑缺乏直接编码这些特性的手段。我们通过一系列映射来应对这一新挑战：i) 将属性图具体化为RDF，ii) 将ProGS映射到SHACL，以及iii) 将G-CORE查询映射到SPARQL CONSTRUCT查询。通过这种方式，属性图的模式推断变得可管理，因为我们通过额外的映射层分解了问题，并利用高效的描述逻辑推理器。我们开发了关于推断模式约束的可靠性以及映射模式与查询的语义等价性的元理论。