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LILT, Dept. of ICS • University of Hawai`i at Manoa • 1680 East-West Road, POST 309 • Honolulu, HI 96822 • 1-808-956-3890

ALVIS (ALgorithm VIsualization Storyboarder)

Chris Hundhausen

Alvis is a new breed of algorithm visualization technology that supports the rapid construction and interactive presentation of "low fidelity" algorithm visualizations.

"Low fidelity" algorithm visualizations differ from conventional "high fidelity" algorithm visualizations in that (a) they do not necessarily illustrate an algorithm for arbitrary input, and (b) they have a rough, unpolished (sketched) appearance. For the theoretical motivations behind this approach, see our research description.

The foundation of ALVIS is SALSA (Spatial Algorithmic Language for StoryboArding), a high-level, interpreted language for programming low fidelity visualizations. Whereas conventional high fidelity AV technology requires one to program a visualization by specifying mappings between an underlying "driver" program and the visualization, SALSA enables one to specify low fidelity visualizations that drive themselves; the notion of a "driver" algorithm is jettisoned altogether. In order to support visualizations that drive themselves, SALSA enables the layout and logic of a visualization to be specified in terms of its spatiality-that is, in terms of the spatial relations (e.g., above, right-of, in) among objects in the visualization.

The ALVIS interactive environment strives to make constructing a SALSA visualization as easy as constructing a homemade visualization out of simple art supplies. To do so, its conceptual model is firmly rooted in the physical metaphor of "art supply" visualization construction. An important component of this metaphor is the concept of cutouts: scraps of virtual construction paper that may be cut out and drawn on, just like real construction paper. In ALVIS, users create storyboards by using a graphics editor (Figure 1b) to cut out and sketch cutouts, which they lay out in the Storyboard View by direct manipulation. They then specify, either by direct manipulation or by directly typing in SALSA commands, how the cutouts are
to be animated over time.

Likewise, ALVIS strives to make presenting a SALSA visualization to an audience as easy and flexible as presenting an "art supply" visualization. To that end, ALVIS's presentation interface supports four features that are taken for granted in "art supply" presentations, but that are notably absent in conventional AV technology. First, using ALVIS's execution interface, a presenter may reverse the direction of storyboard execution in response to audience questions and comments. Second, ALVIS provides a conspicuous "presentation pointer" with which the presenter and audience members may point to objects in the storyboard as it is executing. Third, ALVIS includes a "mark up pen" with which the presenter and audience members may dynamically annotate the storyboard as it is executing. Finally, presenters and audience members may dynamically modify a storyboard as it is executing by simply inserting SALSA commands at the current insertion point in the script.