A dataset is the set of data built from the result of a query, and can optionally have filters applied to it. A dataset contains not only DBFields, but also any formulas, summaries, and parameters that use the DBFields.
A dataset has a name, which by default is the name of the resource on which it is created. You can view items in a dataset by choosing the Dataset View mode from the toolbar of the Resource View panel.
When you create a data component, you specify whether a new dataset is created for it or an existing one is used. Having data components use an existing dataset whenever possible will have a dramatic effect on the performance of your reports in the runtime environment. This is because each dataset is created by running a query against the database, and that is the most expensive part of running a report in terms of execution time.
This chapter describes the following topics related to datasets: