Knowra Datalog Datalog Datalog is a declarative logic programming language that derives relations from facts and rules. Its restricted rule structure supports finite evaluation and makes recursive queries practical.
Horn clause : A logical clause with at most one positive literal, used to express rules in logic programming. Datalog rules are commonly written as Horn clauses whose conclusions follow from their premises.
Relational model : A data model that represents information as relations, commonly displayed as tables. Datalog predicates denote relations, and their arguments correspond to relation attributes.
Recursive query : A database query whose definition refers, directly or indirectly, to itself. Datalog provides a clear rule-based way to compute recursive query results.
Prolog : A logic programming language that uses Horn clauses and goal-directed execution. Prolog permits richer control and term structures, while Datalog favors restricted rules and database-style evaluation.
Unification : A process that finds substitutions making two symbolic expressions identical. Rule variables match facts through substitutions during query evaluation.
Relational algebra : A formal system of operations for querying and transforming relations. Many nonrecursive Datalog rules express relational operations such as joins and projections.
Deductive database : A database system that derives new information from stored facts using logical rules. Datalog rules turn database facts into additional, queryable relations.
SQL : A language for defining, querying, and manipulating relational databases. SQL is the familiar relational alternative, though recursive Datalog rules offer a distinct logical formulation.
Fixed-point semantics : An interpretation of recursive definitions as the least stable solution of repeated application. Repeatedly applying Datalog rules reaches the least fixed point containing all derived facts.
First-order logic : A formal language for statements about objects, relations, and quantifiers. Datalog draws on logical rules while restricting syntax to support effective computation.
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