Parallelizing Plan Recognition

Modern multi-core computers provide an opportunity to parallelize plan recognition algorithms to decrease runtime. Viewing the problem as one of parsing and performing a complete breadth first search, makes ELEXIR (Engine for LEXicalized Intent Recognition)(Geib 2009; Geib & Goldman 2011) particularly suitable for such parallelism. This paper documents the extension of ELEXIR to utilize such modern computing platforms. We will discuss multiple possible algorithms for distributing work between parallel threads and the associated performance wins. We will show, that the best of these algorithms will provide close to linear speedup (up to a maximum number of processors), and that features of the problem domain have an impact on the speedup.