Compositional Evaluation of W3C SPARQL Algebra via Reduce/Map "Tested against older DAWG testsuite. Implemented using functional programming idioms: fold (reduce) / unfold (map)
Does that suggest parallelizable execution?"
Thanks to SPARQL's adoption of compositional semantics (algebra) it's possible. From what I can remember, while there is an implicit left to right evaluation of OPTIONAL, which does limit the top level execution, the partial results are parallelizable. Being able to execute order independent OPTIONAL while retaining the correct results for OPTIONAL is still an open question (although feasible I think).
Available from SVN here. More musings, Musings of a Semantic / Rich Web Architect: What's Next?.