Index Structures for Efficient Querying of Distributed Triplestores

Data is dynamically structured by nature and can be highly diverse and multifaceted. Often, such diverse and complex information needs to be linked. Conventional data-stores, such as relational databases, do not conveniently accommodate dynamically varying structures, as frequently modifying database schemas is not feasible. RDF triplestores offer a flexible solution for handling such data, where any property about an entity can be described by a triple having a subject, a predicate, and an object. Also, data is inherently distributed due to origination points, ownership and many other reasons. Furthermore, storing data in triplestores gives rise to the need to distribute data due to the large number of triples that would result by migrating existing data from a database, for example. In this paper, we present our work on designing index structures in order to facilitate efficient querying of a distributed triplestore (DTS). The distributed querying algorithm in DTS makes use of a sub-graph isomorphism approach to eliminate traversing edges between triplestores that does not have the potential to produce any results. We show that our triplestore has equivalent performance as 3Store when used in a non-distributed mode. Our performance tests in the distributed mode show that the indexes improve efficiency of querying.