Data Access and Transactions

ADO and RDS

ADO and Remote Data Service (RDS) use OLE DB providers to communicate with local and remote data sources respectively. Any application that uses ADO objects gets its data indirectly from OLE DB. If there is an OLE DB provider for it, the data is accessible through ADO.

You can use ADO to write both server-side and client-side applications that can access and manipulate data. ADO, designed to provide a universal high-level data access method, is a collection of Automation objects that can retrieve, update, and create records from any OLE DB provider.

ADO exposes a set of functions that all data sources are expected to implement. Using these core functions, ADO can access the unique features of specific data sources through OLE DB. Additionally, unlike earlier data access methods, you no longer need to navigate through a hierarchy to create objects. You can create most ADO objects independently and reuse them in different contexts. If used correctly, the result is fewer ADO object calls and a smaller working set.

There’s a downside to all this flexibility, however. Because ADO is an OLE DB consumer, the peculiarities of the OLE DB provider that you are using directly influence the behavior of ADO. Just because you can write an application in ADO doesn’t mean that the provider will support it. Often, ADO errors are a direct result of performing operations not supported by the OLE DB provider, or the underlying data source. As you develop database access components and applications, keep in mind that there are sometimes multiple ways to perform any given action.

RDS is a feature of ADO that facilitates client-side programming by optimizing the transfer of data between the client and the ADO components in the middle tier of a Web application. RDS uses ADO as a programming interface between the code and the data exposed by the underlying OLE DB provider. The client-side components of RDS are Microsoft® ActiveX® controls that use either Microsoft® Component Object Model (COM) components or Hypertext Transfer Protocol (HTTP) to communicate with the server components. Microsoft® Internet Explorer includes the RDS client-side components.

Note For Microsoft® Internet Explorer 3.x users, MDAC 2.0 provides service components that are compatible with RDS server-side and client-side components. Client-side components are included with Microsoft® Internet Explorer 5. Since later versions of MDAC are not 100 percent compatible with earlier versions of the browser, you might need to upgrade your clients before using the more advanced features of RDS and ADO.

A detailed look at RDS and ADO is included in the topic Client-Side Data Access later in this section.