Hartig, Olaf. “Foundations of RDF⋆ and SPARQL⋆ (An Alternative Approach to Statement-Level Metadata in RDF).” AMW (2017). The term statement-level metadata refers to a form of data that captures information about another piece of data representing a single statement or fact. A typical example are so called edge properties in graph databases; such an edge property takes the form of a key-value pair that captures additional information about the relationship represented by the edge with which the key-value pair is associated While the Resource Description Framework (RDF) [1] presents another graph- based approach to represent statements about entities and their relationships, its triple- based data model does not natively support the representation of statement-level meta- data. To mitigate this limitation the RDF specification introduces the notion of RDF reification which can be used to provide a set of RDF triples that describe some other RDF
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Abstract: In this systems paper, we present MillenniumDB: a novel graph database engine that is modular, persistent, and open source. MillenniumDB is based on a graph data model, which we call domain graphs, that provides a simple abstraction upon which a variety of popular graph models can be supported. The engine itself is founded on a combination of tried and tested techniques from relational data management, state-of-the-art algorithms for worst-case-optimal joins, as well as graph-specific algorithms for evaluating path queries. In this paper, we present the main design principles underlying MillenniumDB, describing the abstract graph model and query semantics supported, the concrete data model and query syntax implemented, as well as the storage, indexing, query planning and query evaluation techniques used. We evaluate MillenniumDB over real-world data and queries from the Wikidata knowledge graph, where we find that it outperforms other popular persistent graph da