Processing SPARQL Property Path Queries Online with Web Preemption

SPARQL property path queries provide a succinct way to write complex navigational queries over RDF knowledge graphs. However, the evaluation of these queries over online knowledge graphs such as DBPedia or Wikidata is often interrupted by quotas, returning no results or partial results. To ensure complete results, property path queries are evaluated client-side. Smart clients decompose property path queries into subqueries for which complete results are ensured. The granularity of the decomposition depends on the expressivity of the server. Whatever the decomposition, it could generate a high number of subqueries, a large data transfer, and finally delivers poor performance. In this paper, we extend a preemptable SPARQL server with a partial transitive closure operator (PTC) based on a depth limited search algorithm. We show that a smart client using the PTC operator is able to process SPARQL property path online and deliver complete results. Experimental results demonstrate that our approach outperforms existing smart client solutions in terms of HTTP calls, data transfer and query execution time.