MDAC 2.5 SDK - OLE DB Programmer's Reference
Chapter 24: Multidimensional Expressions
Some providers derive the cube implicitly from the specified axis and slicer dimensions. For such providers, there is no need to specify a cube name in the FROM clause. Support for implicitly deriving a cube name from the rest of MDX is an optional feature: It is not required for compliance with OLE DB for OLAP.
To determine whether or not a data source object supports this feature, consumers can check to see if the MDPROPVAL_MJC_IMPLICITCUBE bit is set in the data source property MDPROP_MDX_JOINCUBES.