Datalog
Datalog is a declarative query language for relational databases based on the Logic Programming paradigm. From a syntactical standpoint, an important difference between Datalog and logic programs is that function symbols are not allowed in Datalog. One of the peculiarities that distinguishes Datalog from query languages like Relational Algebra and calculus is recursion, which gives Datalog the capability to express queries like computing a graph transitive closure.