Hi Sanjeewan,
When we talk of processing a cube, there are two parts to it, processing data which rebuilds dimensions with attribute store, hierarchy store and fact data store and processing indexes which creates bitmap indexes and defined aggregation.
ProcessIndexes - Applies to dimension, cube, measure group, and partition. It requires that the object must already have its "data" built; otherwise, it raises an error. ProcessIndexes preserves the data and rebuilds the "indexes". For dimensions, it builds
the bitmap indexes. For partitions, it builds the aggregation data and bitmap indexes. ProcessIndexes is recursively applied to all descendants of the object as well.
Reference:
Different Kinds of SSAS Processing
Bitmap index
Regards,
Charlie Liao
TechNet Community Support
