MDAC 2.5 SDK - OLE DB Programmer's Reference
Chapter 22: OLE DB for OLAP Objects and Schema Rowsets

Semantics of DBGUID_DEFAULT

OLE DB defines a special language dialect identifier, DBGUID_DEFAULT, that denotes the default language dialect. In the context of OLE DB for OLAP, the following semantics apply to the use of this identifier:

• If the provider is both a TDP and an MDP, it must interpret the command string as SQL when DBGUID_DEFAULT is passed as the dialect identifier.
  
  
• If the provider is an MDP, it must interpret the command string as MDX when DBGUID_DEFAULT is passed as the dialect identifier.

Note   Multidimensional consumers are strongly discouraged from using DBGUID_DEFAULT for creating datasets. They must use DBGUID_MDX.