Lecture Database system concepts (6/e): C - Silberschatz, Korth, Sudarshan

Appendix C - Other relational languages, first presents the relational query language Query-by-Example (QBE), which was designed to be used by non-programmers. In QBE, queries look like a collection of tables containing an example of data to be retrieved. The graphical query language of Microsoft Access, which is based on QBE, is presented next, followed by the Datalog language, which has a syntax modeled after the logic-programming language Prolog.