A data set is an object that defines all the data that is available to a report. To create a data set, you must have an existing BIRT data source. As with data sources, BIRT Report Designer provides wizards to create data sets. The first and the only required step in creating a data set is to select the data to retrieve from a data source. After this first step, you can optionally process the raw data as needed for the report. You can, for example, change the names of columns, create computed columns, and define filters to provide a subset of the data to the report.