Split4Blank: Maintaining consistency while improving efficiency of loading RDF data with blank nodes

In life sciences, accompanied by the rapid growth of sequencing technology and the advancement of research, vast amounts of data are being generated. It is known that as the size of Resource Description Framework (RDF) datasets increases, the more efficient loading to triple stores is crucial. For example, UniProt's RDF version contains 44 billion triples as of December 2018. PubChem also has an RDF dataset with 137 billion triples. As data sizes become extremely large, loading them to a triple store consumes time. To improve the efficiency of this task, parallel loading has been recommended for several stores. However, with parallel loading, dataset consistency must be considered if the dataset contains blank nodes. By definition, blank nodes do not have global identifiers; thus, pairs of identical blank nodes in the original dataset are recognized as different if they reside in separate files after the dataset is split for parallel loading. To address this issue, we propose the Split4Blank tool, which splits a dataset into multiple files under the condition that identical blank nodes are not separated. The proposed tool uses connected component and multiprocessor scheduling algorithms and satisfies the above condition. Furthermore, to confirm the effectiveness of the proposed approach, we applied Split4Blank to two life sciences RDF datasets. In addition, we generated synthetic RDF datasets to evaluate scalability based on the properties of various graphs, such as a scale-free and random graph.