What are Semi-additive and factless facts?And in which scenario will you use such kinds of fact tables?

Additive:-- That is the facts which can be aggregated or segregated on the change of the dimension level and always remains meaningful: example: sales value

Now a days almost all data warehouses contain Additrivev facts

Semiadditive fact : That is the facts which can be aggregated or segregated on the change of the dimension level but becomes meaningless on aggregation or segregation

Ex : Gross profit percentage.

These can be represented while u use Customized OLAP

Nonadditive facts: That is the facts which Can Not be aggregated or segregated on the change of the dimension level and always remains meaningful:

Example: at the time of accident near C.N .Tower weather was HOT

Hot is non additive dimension.

(you can call me if you are serious to implement semiadditive and nonadditive fact)