About 4QL

  • 4QL is a rule-based database query language with negation allowed in premisses and conclusions of rules.
  • 4QL is the first such language with tractable and at the same time intuitive semantics, even though the area of deductive databases is over 30 years old.
  • 4QL is founded on a four-valued semantics with truth values: true, false, inconsistent and unknown.
  • 4QL supports a modular and layered architecture and provides a tractable framework for many rule-based forms of reasoning both monotonic and nonmonotonic.
  • 4QL is tractable w.r.t. data complexity and captures all tractable queries.
  • 4QL deals with incomplete and inconsistent information, allowing users to reduce unknown and inconsistent zones by simple constructs, providing means for a uniform treatment of:

    • Open and Local Closed World Assumption (thus also Closed World Assumption),
    • other nonmonotonic/commonsense formalisms, including various variants of default reasoning, autoepistemic reasoning and other formalisms
    • application-specific disambiguation of inconsistent information, including defeasible reasoning.
  • 4QL is therefore well-suited for applications, including:

    • web and Semantic Web services and agents,
    • multiagent systems,
    • advanced ontologies, employing commonsense reasoning techniques,
    • distributed knowledge bases,
    • (distributed) knowledge fusion,
    • robotics systems.