Structure, Abstraction, and Direct Manipulation in Diagram Editors

Editors for visual languages should be as simple and convenient to use as possible; at the same time, programmers should be able to create such editors without prohibitive effort. We discuss the benefits that can be gained from combining the following aspects in an editorgenerator approach: direct-manipulation editing (as in drawing programs)structure-based editing (as in common diagram tools)structural analysis and a common formal model As a major practical example, we present an editor for UML class diagrams. We show that direct-manipulation editing capabilities can enhance the usability of such an editor in comparison to standard tools. A further improvement is obtained by including selective abstraction features similar to the well-known “fisheye-viewing” and “semantic zooming” paradigms. We show that the proposed generator architecture provides an excellent base for implementing such features. The resulting technique can be applied to a wide range of different diagram languages; in contrast to other general solutions, it takes into account the abstract structure and specific abstraction features of the individual languages.