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detail typically includes only element names, while an implementation view
includes visibility, multiplicity, and type information.
The Mylyn project at Eclipse provides a capability to filter out “noise” in an
Eclipse workspace based on what the developer is actively working on. Tasks are
associated with workspace elements that remain visible, while other elements are
dimmed or hidden altogether. Some discussion regards the application of Mylyn
technology to diagrams, although nothing has yet been developed. Contributions
to this area would be welcome because extending this metaphor to modeling in
general has great potential.
GEF provides layering in diagrams, although not much has been done to
exploit this mechanism to “lift” or “lay down” information on a diagram, as was
done historically with transparencies using overhead projectors and today with
presentation animation effects. We need a more well-defined way of defining dia-
grams of multiple layers, which could come in handy when considering the dec-
oration of models as they move from more abstract to more concrete during
model-driven software-development scenarios. This and other ideas to improve
the filtering and rationing of information presented on a diagram are points to
seriously consider when defining your notation, along with an effective layout
algorithm.
4.1.3 Layout
Arguably, the most important factor in providing usable diagrams is layout.
Layout algorithms are numerous and can be tuned to suit a specific notation,
although sometimes custom layouts must be developed. Keep in mind that fixed
or semifixed layouts might be the best option for certain types of diagrams. Our
mindmap diagram uses an automatic layout because the last thing the
Practitioner wants to do while rapidly brainstorming is stop to adjust the posi-
tion of a topic using the mouse. At the same time, class diagram layouts are fairly
mature but still cannot suit the needs of each modeler, so this requires the capa-
bility to adjust the position of diagram elements. Not many modelers would be
satisfied with a fixed-layout class diagram.
Links cause the difficulty in layout, in most cases. Links that cross are often
considered bad form, yet jumps in links that cross are not a great solution, either.
Consider using ellipses (…) to show that a link exists but is not shown until
selected or after a filter is removed. Another possibility is to make visible certain
types of links during mouseover events, allowing a diagram to easily be viewed
in detail but only when desired.
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