Earlier application COM components may have used the data access technologies Remote Data Objects (RDO), and Data Access Objects (DAO).
Briefly described, RDO is an object-oriented data access interface to ODBC combined with the easy-to-use style of DAO. It provides an interface that exposes virtually all of ODBC's low-level power and flexibility. RDO doesn't access Jet or ISAM databases very well, and it can access relational databases only through existing ODBC drivers. However, in the past, RDO has proven to be the interface of choice for a large number of SQL Server, Oracle, and other large relational database developers.
DAO was the first object-oriented interface that exposed the Microsoft Jet database engine (used by Microsoft Access) and allowed Visual Basic developers to directly connect to Access tables — as well as other databases — through ODBC. DAO is suited best for either single-system applications or for small, local deployments.
To summarize, ADO is an object model for accessing all types of data through OLEDB, RDO is an object model for accessing relational data through ODBC, and DAO is an object model for accessing local or SQL data through Jet. All are COM interfaces and can be used from a variety of tools, including Microsoft Visual Basic, Microsoft Access, and Microsoft Office.