Editing graphic models always entails layout problems. Inserting and deleting items requires tedious manual work for shifting existing items and rearranging the diagram layout. Hence, techniques that automatically expand a diagram when space is required for insertion and contract it when free space becomes available are highly desirable. Existing layout generation algorithms are no good solution for that problem: they may completely rearrange a diagram after an editing operation, while users want to preserve the overall visual appearance of a diagram. We have developed a technique which automatically expands or contracts a diagram layout when items are inserted or removed while preserving its overall shape, i.e. the positions of the items relative to each other. Our technique has been implemented in a prototype tool. We are using it not just for simplifying editing, but primarily for implementing an aspect-oriented visualization concept.
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