Section: New Results

Efficient query answering over semantic graphs

Query answering in RDF knowledge bases has traditionally been performed either through graph saturation, that is, adding all implicit triples to the graph, or through query reformulation, i.e. modifying the query to look for the explicit triples entailing precisely what the original query asks for. The most expressive fragment of RDF for which reformulation-based quey answering exists is the so-called database fragment of RDF (Goasdoué et al., EDBT 2013), in which implicit triples are restricted to those entailed using an RDFS ontology. Within this fragment, query answering was so far limited to the interrogation of data triples (non-RDFS ones); however, a powerful feature specific to RDF is the ability to query data and schema triples together. In [12], we address the general query answering problem by reducing it, through a pre-query reformulation step, to that solved by the query reformulation technique mentioned above (EDBR 2013). Our experiments also demonstrate the very modest cost (performance overhead) of this more powerful (more expressive) reformulation algorithm.