This chapter describes how the Microsoft SQL Server version 7.0 query processor interacts with an OLE DB provider to enable distributed and heterogeneous queries. It is primarily intended for OLE DB provider developers, and assumes a good understanding of the OLE DB specification. The emphasis is on the OLE DB interface between the SQL Server query processor and the OLE DB provider, not on the distributed query functionality itself. For a full description of distributed querying functionality, see SQL Server Books Online.