Common Logic (CL) is a framework for a family of logic-based languages with the purpose of standardizing syntax and semantics for information interchange. It is a work in progress towards an ISO standard (currently - at the end of 2006 - ISO Draft). There are three syntaxes standardized:
- CLIF - Common Logic Interchange Format, based on KIF
- CGIF - Conceptual Graph Interchange Format
- XCL - eXtended Common Logic Markup Language, based on XML
Each CL feature has a concrete expression in these three syntaxes; in other words, any statements in any of these languages can be translated to any other language while preserving the original semantics. Common Logic model theory supports first order predicate logic, and so can be used for exchanging first order formulas in a standardized form. It also supports some features of higher order logics, such as quantifying over predicates specified in the domain of discourse (not over any possible predicates).
This project is similar to the Ontolingua project in a sense that it aims to propose interchange format, however it is more focused on logic-based languages and builds its semantics on the first order predicate logic. It also proposes multiple syntactic forms to be used for expressing the same knowledge. Also, it should become official ISO standard.