Datalog is a fundamental rule language for knowledge representation. A Datalog rule is a logical implication, where both the "if" part of the implication (the rule body) and the "then" part of the implication (the rule head) consist of a conjunction of conditions. In the context of RDF, a Datalog rule conveys the idea that, from certain combinations of triples in the input RDF graph, we can logically deduce that some other triples must also be part of the graph.