MDAC 2.5 SDK - OLE DB Programmer's Reference
Chapter 23: Rowsets in OLE DB for OLAP

Creating an Accessor to Fetch Data

Before fetching cell data, the application has to create an accessor that describes the structure of the data buffer. This is done using the IAccessor::CreateAccessor method. The accessor created using this method is given as an input parameter to the IMDDataset::GetCellData method. Because GetCellData can fetch multiple cells in a single call, the provider must know the size of each cell in the data buffer. Applications must provide this size in the cbRowSize argument of the IAccessor::CreateAccessor method. Failure to do so will result in an error from this method, and an accessor will not be created.