BitMat: A Main Memory RDF Triple Store.
(January 2009)Abstract
BitMat is a main memory based bit-matrix structure for representing a large set of RDF triples, designed primarily to allow processing of conjunctive triple pattern (join) queries. The key aspects are as follows: i) its RDF triple-set representation is compact compared to conventional disk-based and existing main-memory RDF stores, ii) basic join query processing employs logical bitwise AND/OR operations on parts of a BitMat, and iii) for multi-joins, intermediate results are maintained in the form of a BitMat containing candidate triples without complete materialization, thereby ensuring that the intermediate result size remains bounded across a large number of join operations, provided there are no Cartesian joins. We present the key concepts of the BitMat structure, its use in processing join queries, describe our experimental results with RDF datasets of different sizes (from 200k to 47 million), and discuss the use case scenarios.