MDAC 2.5 SDK - OLE DB Programmer's Reference
Chapter 22: OLE DB for OLAP Objects and Schema Rowsets
Many providers generate the values of _UNIQUE_NAME columns by concatenating several names. For instance, the unique name of a level might be <dim_name>.<hier_name>.<level_name>. In such a case, the provider might not be able to report the maximum sizes of such columns (when methods on the IColumnsInfo interface are called to determine a size). If the provider is unable to determine the maximum column size, it returns a size of ~0 (all the bits are set to 1) to indicate that it is unable to accurately determine the size.