F-logic

F-logic (frame logic) is a knowledge representation and ontology language. F-logic combines the advantages of conceptual modeling with object-oriented, frame-based languages and offers a declarative, compact and simple syntax, as well as the well-defined semantics of a logic-based language. Features include, among others, object identity, complex objects, inheritance, polymorphism, query methods, encapsulation. F-logic stands in the same relationship to object-oriented programming as classical predicate calculus stands to relational database programming.

F-logic was developed by Michael Kifer at Stony Brook University and Georg Lausen at the University of Mannheim. F-logic was originally developed for deductive databases, but is now most frequently used for semantic technologies, especially the Semantic Web. F-logic is considered as one of the formalisms for ontologies, but description logic (DL) is more popular and accepted, as is the DL-based OWL.

A development environment for F-logic was developed in the NeOn project and is also used in a range of applications for information integration, question answering and semantic search. Prior to the version 4 of Protégé ontology editor, F-Logic is supported as one of the two kinds of ontology.