Once we have a general understanding of the data involved in the application, we can decide what data is going to be in the input variables and what will be the role of each one of them. It is important to consider that input and output variables are not mutually exclusive; a variable can be used both as a part of an input and an output. Input widgets can also have different roles. They can be used as filters, aggregate variables, variables selectors for visualizations, and so on. In other words, they can be used as inputs for almost any process that can be programmed within a reactive context.

This flexibility enables us at this preprogramming stage to conceive an application with almost no restrictions. Although this is definitely an advantage, it has to be handled carefully. The need to develop an application that covers every possible aspect of the dataset, although technically possible, can produce a very confusing outcome. It is important to keep in mind that these...