About 4ql
- 4QL is a rule-based database query language with negation allowed in premises 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 wrt 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 belief bases,
- (distributed) belief fusion,
- robotics systems.
