Design Constraints

Our basic design constraints are the elements of a spreadsheet that we consider to be ``non-negotiable''. Let us discuss these below.

• The tabular layout has proven useful in numerical spreadsheets, and has a number of advantages. First, it enables users to enter data into cells in various configurations. Second, because of its easy-to-comprehend structure, the cells are easily to navigate to and from. Third, because it affords easy grouping, operations can be defined on rows and columns, or portions of a spreadsheet.
• Cells are adapted to handle large datasets instead of a few numbers. They handle visual representations of complex data-types with text strings, hierarchical structures, and regular and irregular shapes. These cells may contain references to other datasets in other cells. Because spreadsheets now contain groups of large datasets, users can now see much more than just a single dataset in an established context.
• Since the datasets are no longer just simple numbers, the operations now consist a variety of operators for different types of datasets. Certain operators may take columns, rows, or a subgroup of cells as operands. Alternatively, operators may distribute their operation across a group of cells. Because the primary elements are visual, the vocabulary for the spreadsheet is richer. This also results in more difficulties in the design of the user interface for these operations.

One additional philosophical assumption is that since users are accustom to to the spreadsheet metaphor, we expect user skills in numerical spreadsheets to transfer easily to the visualization spreadsheet. The existence of a variety of operators may thwart this transfer. The challenge is to design a intuitive interface for this wide array of operators. Numerical spreadsheets map operators to textual commands to partially solve this problem. In this paper, we examine both command languages as well as direct manipulation interfaces in an attempt to understand how these two techniques can be used in a spreadsheet interface.