QBD * : a Graphical Query Language with Recursion 1

One of the main problems in the database area is to define query languages characterized by both high expressive power and ease of use. In this paper, we propose a system to query databases, using diagrams as a standard user interface. The system, called Query by Diagram* (QBD*), makes use of a conceptual data model, a query language on this model and a graphical user interface. The conceptual model is the Entity-Relationship Model; the query language, whose expressive power allows recursive queries, supports visual interaction. The main characteristics of the interface are the ease of use, and the availability of a rich set of primitives for schema selection and query formulation. Furthermore, we compare the expressive power of QBD* and G+, which are the only languages allowing recursive queries to be expressed graphically.