Datasheet

Figure 1-2

The main problem with DAO is that it can only talk to the JET engine. The JET engine then communicates

with ODBC to retrieve the data. Going through this extra translation layer adds unnecessary overhead

and makes accessing data through DAO slow.

RDO

Remote Data Objects (RDO) was Microsoft’s solution to the slow performance created by DAO. For talk-

ing to databases other than Microsoft Access, RDO did not use the JET engine like DAO; instead, it com-

municated directly with the ODBC layer. Figure 1-3 shows this relationship.

Removing the JET engine from the call stack greatly improved performance to ODBC data sources. The JET

engine was only used when accessing a Microsoft Access Database. In addition, RDO had the capability to

use client-side cursors to navigate the records, as opposed to the server-side cursor requirements of DAO.

This greatly reduced the load on the database server, enabling not only the application to perform better,

but also the databases on which that application was dependant.

RDO was primarily targeted toward larger, commercial customers, many of whom avoided DAO due to

the performance issues. Instead of RDO replacing DAO, they largely co-existed. This resulted for several

reasons: First, users who developed smaller applications, where performance wasn’t as critical, didn’t

want to take the time to switch over to the new API. Second, RDO was originally only released with the

Enterprise Edition of Visual Basic, so some developers didn’t have a choice. Third, with the release of

Data Store

Application

DAO

JET Engine

ODBC

MS Access

History of Data Access

03_584375 ch01.qxd 10/28/05 10:49 PM Page 7