Comparison of geospatial support in RDF stores: Evaluation for ICOS Carbon Portal metadata

Abstract: The evolution of World Wide Web (WWW) into semantic web is happening with the aid of standards like Resource Description Framework (RDF), SPARQL and a few others from World Wide Web Consortium (W3C). Over the years, semantic data management technologies have been introduced as software platforms commonly known as RDF stores. Lately these RDF stores have been tested for processing and maintenance of large data sets complying with Linked Data principles. In order to standardize geographic capabilities in these RDF stores, Open Geospatial Consortium (OGC) adopted GeoSPARQL as an extension to SPARQL query. Our study aims to discuss the geospatial capabilities, and the conformance to GeoSPARQL standard, of the five RDF stores: Eclipse RDF4J 2.4.0, Apache Jena 3.9.0, Openlink Virtuoso 7.2.4, Stardog 6.0.1 and GraphDB 8.8.0. Along with the investigation of features, the performance evaluation of these RDF stores has also been conducted by measuring the execution times of a set of GeoSPARQL queries. The evaluation query set consists of non- topological, spatial selection as well as spatial join queries adopted from a spatial benchmark, Geographica. The geospatial component of Integrated Carbon Observation System (ICOS) Carbon Portal (CP) metadata has been used for performance evaluation in order to establish the suitability of the RDF stores for ICOS-CP requirements. Java Programs have been developed in order to interact with all the RDF stores for upload of data and execution of benchmark queries. Some result set disparities amongst the RDF stores as well as variation in performance metrics on different hardware platforms have also been highlighted in our research.