Query Engine

A Query Engine is a software component positioned on the top of a database e.g., a relational database such as MySQL or a triplestore such as Blazegraph, etc., that is in charge of implementing query functionalities against data stored in the database and providing answers to users and applications.

Query Engine in Semantic MediaWiki
Semantic MediaWiki provides support for relational databases, triplestores and Elasticsearch offering Query Engines. The latter only serves as a query engine while the others also serve as Storage Engine at the same time.