Deductive Database with Datalog, SQL, RA, TRC, DRC
The Datalog Educational System (DES) is a deductive database with Datalog, SQL, Relational Algebra, Tuple Relational Calculus and Domain Relational Calculus as query languages developed mainly for education. It can be used from most common Prolog interpreters over any supported OS and from portable executables (Windows, Linux and MacOS).
This is a english based query tool. This was worked on for about 5 years before being abandoned in about 1999. The company that I work for agreed to open source the code.