The first layer of abstraction is the Connection. The Connection stores information about how to access the data and what data to make available to Tableau. The connection attributes for the database, the tables, views and columns to use, and any joins or custom SQL used to access the data. To support true ad hoc analysis, Tableau does not require that all fields, tables or joins be included in the initial connection. This allows users to get started with a simple connection and change it as needed to include more fields or tables.