MDAC 2.5 SDK - OLE DB Programmer's Reference
Chapter 6: Getting and Setting Data

Accessors

An accessor is a data structure created by the consumer that describes how row or parameter data from the data store is to be laid out in the consumer's data buffer. For each column in a row (or parameter in a set of parameters), the accessor contains a binding. A binding is a data structure that holds information about a column or parameter value, such as its ordinal value, data type, and destination in the consumer's buffer. When calling a method that transfers data, such as IRowset::GetData, IRowsetChange::SetData, or ICommand::Execute, the consumer passes as parameters to the method an accessor handle (or, when transferring parameter data, a DBPARAMS structure containing an accessor handle) and a pointer into the consumer's data buffer. The provider uses the accessor to determine how to transfer the data to or from the consumer's buffer.

An accessor is identified by its handle, as follows:

typedef ULONG HACCESSOR;