FUNDAMENTAL GRAPHICAL PRIMITIVES FOR VISUAL QUERY LANGUAGES

The need of a friendly man-machine interaction is becoming crucial for a large variety of applications. In order to reach such a friendliness a new class of languages has been proposed (Visual Languages), based on the extensive use of graphical and iconic mechanisms. We are interested in a particular subclass of Visual Languages, called Visual Query Languages (VQLs), devoted to the extraction of information from databases. VQLs are mainly based on the idea of applying new interaction mechanisms, based on the ''direct manipulation'' paradigm, on visually represented databases. Various VQLs have been proposed, but only a few of them are provided with a formal definition and, also when such a formal definition exists, it does not give the semantics of the graphical operations performed by the user. In this paper we aim to provide such a semantics by proposing a graphical data model, the graph model, in which the visual representation is part of the model itself and a minimal set of Graphical Primitives, in terms of which general query operations may be visually expressed. Moreover, we show that: (a) such a model may be used as a general visual representation for the most common data models; (b) the Graphical Primitives have the same expressive power as well-known query languages; (c) the graph model and the Graphical Primitives may be used as basic constituents of more complex existing visual representations and visual query languages, thus giving them a semantics independent from the underlying data model.