1.physical layer 2.business layer 3.presentation layer
Here I am trying to elaborate it:
Database Layer - Tables are imported in this layer.
Model View Layer - All the relationships, renaming of query subjects and query items, resolving loops etc are done in this layer.
Business View layer - This is the view which will be visible to users. We create star schema grouping in Model View and move it to the Business layer view. This layer only contains the shortcuts.