There is another important difference between accessing a fact table and a lookup table. If a value, such as April sales, is missing from a fact table, the row still exists in the table and is reported as null or zero. If that same value is missing in a lookup table, the April row does not exist. The previous or next value (March or May) is reported, depending on whether the level is set to beginning or ending value.

—
Please post your comment on this.