Vensim can use data in two ways. First, as exogenous inputs to drive models, and second, as a basis for comparing the behavior of a model with what actually happened.
Exogenous inputs are known as Data variables and are time series inputs which drive a portion of your model. Data variables are not computed during simulation, but instead refer to an existing data series (time series) for use during simulation. This data series can either be an imported Vensim dataset used by a Data variable in the model, or a time series residing in an external file such as an Excel or 123 spreadsheet used by a Data variable with a Data function in the model.
The second way to use data involves loading real world data as a Vensim dataset, then comparing the dataset against model behavior using the Analysis tools. You must have Microsoft Excel or Lotus 123 installed to complete this chapter.
