An interface for an RDF Storage And Inference Layer. RDF Sails can store RDF
statements and evaluate queries over them. Statements can be stored in named
contexts or in the null context. Contexts can be used to group sets of
statements that logically belong together, for example because they come from
the same source. Both URIs and bnodes can be used as context identifiers.
Opens a connection on the Sail which can be used to query and update data.
Depending on how the implementation handles concurrent access, a call to
this method might block when there is another open connection on this