An Overview of ADO

ADO is Microsoft's universal data-access technology. Universal means that ADO is designed to allow access to any kind of data source imaginable, from a SQL Server database to the Windows Active Directory to a text file saved on your local hard disk, and even to non-Microsoft products such as Oracle. All these things and many more can be accessed by ADO.

ADO doesn't actually access a data source directly. Instead, ADO is a data consumer that receives its data from a lower-level technology called OLE DB. OLE DB cannot be accessed directly using VBA, so ADO was designed to provide an interface that allows you to do so. ADO receives data from OLE DB providers. Most OLE DB providers are specific to a single type of data source. Each is designed to provide a common interface to whatever data its source may contain. One of the greatest strengths of ADO is that, regardless of the data source you are accessing, you use essentially the same set of commands. There's no need to learn different technologies or methods to access different data sources.

Microsoft also provides an OLE DB provider for ODBC. This general-purpose provider allows ADO to access any data source that understands ODBC, even if a specific OLE DB data provider is not available for that data source. Figure 20-2 shows the communication path between ADO and a data source.

ADO OLEDB Provider

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