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).
Web-based (with desktop installation possible) application that helps keep track of and manage a book collection. Working demo (read-only) here: http://www.fraca7.net:8000/books/. Integration with an iPhone version planned.