Data items are classified as keys or results:
A key data item refines the amount of detail in a view and usually results in additional rows returned when a view is refreshed. With the inclusion of each successive key, envision adding the word “per” to a view definition. For example, start with the Page I/O result data item. Refine the granularity by adding the Database key data item, Page I/Os “per” Database. Further refine the granularity by adding the Object key data item, Page I/Os “per” Database “per” Object.
A result data item returns performance data at the level of detail determined by the key data items in a view. If no key data items are specified, only one row of data is returned.
A data item’s designation as a result or key is a characteristic of the data item and is independent of the statistical type associated with the data item in a view.