Certain Answers and Rewritings for Local Regular Path Queries on Graph-Structured Data

In this paper we explore the connection between certain answers and view-based rewritings for local regular path queries (RPQs) which are regular expressions matching paths in graph-structured data starting from a specific node. We show that differently from the case of global RPQs, which match paths starting from any node, the notions of certain answer and rewriting-based answer coincide for local RPQs. The importance of this result is that obtaining the certain answer for local RPQs can be done in polynomial time in the size of the data. We also present an automata-theoretic algorithm for computing maximal view-based rewritings. Notably, these rewritings are an exponential order of magnitude smaller than their counterparts for global RPQs.