Querying APIs with SPARQL: language and worst case optimal algorithms

Abstract

Although the amount of RDF data has been steadily increasing over the years, the majority of information on the Web is still residing in other formats, and is often not accessible to Semantic Web services. A lot of this data is available through APIs serving JSON documents. In this work we propose a way of extending SPARQL with the option to consume JSON APIs and integrate the obtained information into SPARQL query answers, thus obtaining a query language allowing to bring data from the “traditional” Web to the Semantic Web. Looking to evaluate these queries as efficiently as possible, we show that the main bottleneck is the amount of API requests, and present an algorithm that produces “worst-case optimal” query plans that reduce the numberof requests as much as possible. We also do a set of experiments that empirically confirm the optimality of our approach.