How to access and apply operations is an important aspect of the spreadsheet. We examined two different methods for performing spreadsheet operations.
The first method is a direct manipulation interface corresponding to a ``noun-verb'' model, where the user first selects a group of cells (the noun), and then applies an operation (the verb) to those cells. The operation is specified using a combination of menus and dialog boxes. For example, to set up the similarity data in Figure 1, the user first selects a column of cells, then performs a single import operation of a large dataset into those cells. Some example menus and dialog boxes used in SSR system is shown in Figure 4.
Figure 4: Our spreadsheet visualization system for molecular biology
uses a direct manipulation interface with menus and dialog boxes,
which makes the system easy to use.
The second method is a command and script language based interface. The user can interactively enter commands in an entry box, similar to a traditional numerical spreadsheet. Alternatively, she can write a script file and load in the script. For example, she can define a layout by writing a script that specifies the datasets and the representation method used for each cell. The script file can contain other non-layout commands such as animation, or even define new commands. In Figure 2, we can see in the history window, the user has just loaded a script with a pre-defined layout.
The command language can also be used to define modules to extend the spreadsheet, such as file input modules or modules that define a visual representation for a given data type. To use the module, the user simply loads the module, and the new commands in that module become available to her. For example, in Figure 2 the user programmed new modules that implement new representations for matrices using the command language. The command language we defined for the visualization spreadsheet includes operators such as AddCell, SubtractCell, Scatterplot, ReadBioMatrix, and Carpetplot. The operators follow the convention of `` command result arguments'', where command operates on the arguments and puts the outcome in cell result.
From our experience of the two systems, we believe a combination of the two approaches is appropriate for the visualization spreadsheet. The advantages of a menu-based interface are that it is relatively intuitive to use for first-time users, and training time for new users is short. However, because there are many functionalities in a visualization spreadsheet system, there is the danger of creating a large number of menus with no structure to them. Menu systems also tend to slow down frequent knowledgeable users. The advantages of a command language based interface are its flexibility and its appeals to power users. Command languages can also be used to construct macros so complex tasks can be performed rapidly. The disadvantages are that command languages are difficult to master and require substantial training and memorization.
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