Data Access Objects

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Data Access Objects (DAO) were an object oriented interface created by Microsoft which allowed early versions of Microsoft Access and Visual Basic to use the Jet database engine. Later (in version 3.5) it was able to bypass the Jet engine altogether and directly access ODBC data sources, including Microsoft SQL Server and other enterprise database systems. DAO 3.6 was the final version developed by Microsoft. Microsoft says that DAO will not be available in its future 64-bit operating systems.

DAO works by creating a "Workspace" object in which all database operations are performed. The workspace object exists as a session object that exists within a larger database engine object. There are two types of database engines: a Jet database engine object, and an ODBCDirect database engine.

The Jet database engine object consists of several objects: a workspace object and a series of error objects. The workspace object consists of a groups and users object and a database object. The database object consists of container objects which consist of containers of objects, query definition (QueryDef) objects, Recordset objects which are defined by a set of field objects, relation objects which show the relationship between different fields in the database, and table definition (TableDef) objects which consists of fields and indexes of selected fields.

The ODBCDirect database engine consists of a workspace object and an errors object. The main difference between this database engine and the Jet database engine is that the workspace object is different in that it only consists of a series of ODBC connection objects and the database object consists of a series of recordset objects. The ODBC connection objects consist of QueryDef objects and recordset objects.