Guidelines for Using Multiple Views

The first set of guidelines we consider have been proposed by Baldonado et al. [204] to aid the design of multiple views systems. A multiple views system, by their definition,

“uses two or more views to support the investigation of a single conceptual entity.”

The first four guidelines are intended to guide when to use multiple views, whereas the last four guidelines provide advice on how to choose between the several types of view presentations and interactions.

1. “Rule of Diversity: Use multiple views when there is a diversity of attributes, mod-els, user profiles, levels of abstraction, or genres.”

InHyperCell’s case this rule applies because there is a diversity of attributes repre-sented by the several variables of a high-dimensional dataset.

2. “Rule of Complementarity: Use multiple views when different views bring out cor-relations and/or disparities.”

One of the basic objectives ofHyperCellis to help bring out any meaningful corre-lation or interesting behaviour between variables.

3. “Rule of Decomposition: Partition complex data into multiple views to create man-ageable chunks and to provide insight into the interaction among different dimen-sions.”

TheHyperCell relies on the presentation of high-dimensional data as multiple cells as result of the application of one or more filters to the data.

4. “Rule of Parsimony: Use multiple views minimally.”

HyperCell avoids the automatic creation and simultaneous display of all possible subspaces obtained by combining variables. We believe this would overload the user with information that might be not required to the task at hand. Instead Hyper-Cell delegates the responsibility of creating the subspaces to the user.

5. “Rule of Space/Time Resource Optimization: Balance the spatial and temporal costs of presenting multiple views with the spatial and temporal benefits of using the views.”

This rule draws attention to the fine balance between showing all views

simulta-needed to present them. This is one of the reasons we have proposed two different lay-outs of cells – the 2D ‘fruit machine’ and the building lay-out – as explained in Chapter 5, Section 5.4.1. Further discussion on this issue is presented in Sec-tion 7.4, where we present the overall results from applyingHyperCell to the case studies.

6. “Rule of Self-Evidence: Use perceptual cues to make relationships among multiple views more apparent to the user.”

HyperCell follows this rule through the use of linking and brushing, defined by Baldonado et al. as coupled interaction. Other forms of perceptual cues can be created by arranging the multiple views so that similar axes are aligned.

7. “Rule of Consistency: Make the interfaces for multiple views consistent, and make the states of multiple views consistent.”

HyperCell uses the same visual representation for cells with same dimensionality, regardless of the combination of variables. Also we have tried to keep consistency between the representation of variables in the interfaces of IGraph, NDWin, and NDBrush modules. The advantage of using a consistent visual representation for the data is evident in remarks of the case study #3, described in Section 7.3.3.

8. “Rule of Attention Management: Use perceptual techniques to focus the user’s attention on the right view at the right time.”

One of the most important events inHyperCellis the creation of a cell and whenever this happens the last window to pop up is the one that contains the rendering of the cell.

The first four guidelines were fundamental in improving an earlier design of Hyper-Cell which had been implemented for Microsoft Windows environment as a bespoke C++

program using OpenGL (see Figure 7.1). That early version had only two windows: one on the left-hand side containing a tree representation of cells (leaves) and workspaces (roots) created; and, the visualization window on the right-hand side in which the IGraph interface and the visualization of the cells are presented.

The rule of diversity helped us to see the need to assign separate views for the in-terface and for the visualizations produced, since they convey distinct informations. The decomposition rule has lead us to the current HyperCell design in which a workspace is used to accommodate several cells linked to the same region of interest around a fo-cus point, in contrast with the early version whose function was simply to organize the

cells into groups. We felt that by associating location in n-space with a workspace it be-came easier for the users to understand that cells contained in a workspace correspond to ‘slices’ taken from the same location in n-space. This association, in turn, helps the partition of the high-dimensional data space into “manageable chunks”, as suggested by the decomposition rule.

Figure 7.1: Screenshot of an early version of HyperCell.

Therefore the latest HyperCell version is based on a more extensive use of multiple views, supported by the first four guidelines. This version has also tried to follow the last four guidelines (as discussed when the guidelines were introduced on page 130).

However, it seems to comply minimally with the self-evidence and attention management rules.

Regarding the self-evidence rule we believe thelinking and brushingto be very simple for two reasons: 1) it does not allow the user to create the brushing in the visual space (i.e. the rendering window) but only via data space (i.e. the NBrush interface); and, 2) the brushing mechanism only shows a box surrounding the brushed data, not highlighting them nor eliminating the non-brushed data.

With respect to the rule of attention management we felt that making a created cell

“pop up” was a simple feature to satisfy this rule, but that other mechanisms should also