SPQR: SPARQL Processor and Query Rewriter for accessing multiple heterogeneous network measurement repositories

The data heterogeneity in network measurements (in data definition models, data sharing protocols, data processing algorithms, etc) is a known problem and several projects are focused on solving it. In this regard, MOMENT is a Seventh Framework Program European project that is focused on using semantic technologies to access multiple heterogeneous network measurement repositories. In this paper we show one of the main algorithms of the MOMENT architecture, which handles distributed SPARQL repositories by rewriting the queries using optional clauses. By means of a general ontology describing the network measurements domain and semantic wrappers for relational databases, the MOMENT mediator is able to semantically query from a unique access point and transparently to the user, several network measurement repositories like LOBSTER, ETOMIC, DIMES and MOME.