Most data sources give the option of either connecting live or extracting the data; however, some cloud-based data sources do require an extract. Conversely, OLAP data sources cannot be extracted and require live connections.

When using a live connection, Tableau issues queries directly to the data source (or uses data in the cache if possible). When you extract the data, Tableau pulls some or all of the data from the original source and stores it in a Tableau Data Extract file (.tde). Extracts extend the way in which Tableau works with data. Consider the following diagram:

The fundamental paradigm of how Tableau works with data does not change, but you'll notice that Tableau is now querying and getting results from the extract. Data can be retrieved from the source again to refresh the extract. Thus, each extract is a snapshot of the data source at the time of the latest refresh. Extracts offer the benefit of being portable and extremely efficient.