Query by Diagram: a Visual Environment for Querying Databases

In recent years, several attempts have been made to define query languages characterized by both high expressive power and easy query formulation. Several issues concern graphical applications, based on the diagrammatic representation of a semantic model and visual interaction. This paper describes the architecture and the implementation of a graphical query system, based on the diagrammatic representation of entity relationship schemata. The query language underlying the system allows the formulation of recursive queries; moreover, user interaction in both managing diagrams and expressing queries is simplified by the presence of a fully visual environment and a rich set of interaction strategies.