The application programming interface (API) is the mechanism that the application uses to communicate with the database engine interface. The API interface may be visible or invisible. For example, the application may be a true client (as in client/server) that communicates with a Windows SQL Server. In other cases, the application may be a pseudo-client (as in a file server). Examples of pseudo-clients are Visual Basic or Microsoft Access using a Microsoft Access database and Open Database Connectivity (ODBC) connections to xBase or Paradox™.