Dimension tables are expected to store columns that cannot be aggregated whereas fact tables are expected to store measure columns that can be aggregated.
As a general rule:
Unlike relational fact tables, logical fact tables can contain measures of different grains. Because of this, grain is not a reason to split up logical fact tables.
Aggregate sources should be created as separate logical table sources. For fact aggregates, use the Content tab of the Logical Table Source dialog to assign the correct logical level to each dimension.
Fact sources are selected on a combination of the fields selected as well as the levels in the dimensions to which they map.
OBIEE - (Fragment|ation) (Partitioning):
The following is a list of the types of fact tables that OBIEE recognizes when using the project feature: