The data access layer is the simplest layer of the traditional three-tiered architecture.
Simply put, the data access layer calls stored procedures that reside in the database or executes dynamic
SQL against the database. In prior versions of the .NET Framework, as the developer you were responsible for making sure that you knew which type of ADO.NET object should execute a stored procedure
and what type of object should be passed back to the business layer. The debate about which object to
pass back to the business layer is always heated, but the .NET Framework has given us a tool that could
calm those debates.