What is the difference between the Pellet and Jena query engines?
The Jena query engine is RDF triple based, so to produce variable bindings it works one triple at a time. In contrast, the Pellet query engine considers the entire conjunctive query. This difference causes the engines to have different performance characteristics and in some cases yields different results. First, by using a level of representation consistent with the logic, the Pellet query engine can perform optimizations that are inaccessible to the Jena query engine. These optimizations often yield a significant speed-up in query answering. Second, results may differ based on handling of blank nodes in queries. The semantics of SPARQL are such that blank nodes need not be bound to asserted individuals and can match individuals that are inferred (such as those from existential restrictions and minimum cardinality constraints). The Pellet engine will produce results using these inferred individuals and the Jena engine will not. An example demonstrating how this can change results is i
