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Chapter 27. Understanding Universal Data... > Interfacing with a Wide Range of Dat...

Interfacing with a Wide Range of Data Sources

Today's most popular methods of connecting with sources of data are the ODBC API, and DAO. Thirty-two-bit ODBC drivers now are available for virtually every client/server RDBMS; most popular Indexed Sequential Access Method (ISAM) databases (Jet, dBase, FoxPro, and Paradox); spreadsheets (Excel); and delimited text files. Microsoft Office traditionally has relied on ODBC drivers for most of its database connectivity features. Although other software publishers attempted to introduce ODBC alternatives, ODBC quickly became the de facto standard of the database industry. ODBC is a C/C++ API; making direct use of the ODBC API in Access applications requires a large number of VBA function prototype declarations (DECLAREs) and heavy-duty, low-level coding. Few, if any, Access developers access the ODBC API directly.

In 1994 Microsoft Access 2.0 introduced 16-bit DAO in conjunction with version 2.0 of the Jet database engine. Like ODBC, the Jet database engine is a C/C++ API. DAO provided what was then called an OLE Automation wrapper over the Jet API; up to that time OLE had been used primarily for creating and manipulating compound documents. DAO exposes a complex hierarchy of programmable data-related objects with the DBEngine object at the top. Lower objects in the hierarchy, Workspaces, Databases, TableDefs, QueryDefs, and Recordsets, are object layers under DBEngine. Jet databases permit attaching other databases via ODBC, eliminating the need for low-level ODBC API programming. 32-bit Jet and DAO 3.0 appeared with the release of Access 95; Access 2000 introduces Jet 4.0 and DAO 3.6. Microsoft has sold tens of millions of Access licenses, making Jet the most widely used desktop database in the world and DAO the default database object model for Access users and for the majority of Access and Visual Basic programmers.


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