Any data source that is using an extract will have a distinctive icon that indicates the data has been pulled from an original source into an extract, as shown in the following screenshot:

The first data connection in the preceding data pane is extracted, while the second is not. After an extract has been created, you may choose to use the extract or not. When you right-click a data source (or Data from the menu and then the data source), you will see the following menu options, as demonstrated in this screenshot:

1. Refresh: The Refresh option under the data source simply tells Tableau to refresh the local cache of data. With a live data source, this would requery the underlying data. With an extracted source, the cache is cleared and the extract is requeried, but this Refresh option does not update the extract from the original source. To do that, use Refresh under the Extract sub-menu (see step 4 in this list).
2. Extract data...: This creates a new extract from the data source (replacing an existing extract if it exists).
3. Use Extract: This option is enabled if there is an extract for a given data source. Unchecking the option will tell Tableau to use a live connection instead of the extract. The extract will not be removed and may be used again by checking this option at any time. If the original data source is not available to this workbook, then Tableau will ask where to find it.

4. Refresh: This Refresh option refreshes the extract with data from the original source. It does not optimize the extract for some changes you make (such as hiding fields or creating new calculations).
5. Append data from file...: This option allows you to append additional files to an existing extract, provided they have the same exact data structure as the original source. This adds rows to your existing extract; it will not add new columns.
6. Optimize: This will restructure the extract, based on changes you've made since originally creating the extract, to make it as efficient as possible. For example, certain calculated fields may be materialized (that is, calculated once so that the resulting value can be stored) and newly hidden columns or deleted calculations will be removed from the extract.
7. Remove: This removes the definition of the extract, optionally deletes the extract file, and resumes a live connection to the original data source.
8. History: This allows you to view the history of the extract and refreshes.
9. Properties: This enables you to view the properties of the extract, such as the location, underlying source, filters, and row limits.