The Type 1 Dimension mapping filters source rows based on user-defined comparisons and inserts only those found to be new dimensions to the target. Rows containing changes to existing dimensions are updated in the target by overwriting the existing dimension. In the Type 1 Dimension mapping, all rows contain current dimension data.
For example, you might have a site dimension table with store code, location, and overhead that you update after the company opens a new store. This dimension is used for sales and overhead calculations. Since you do not need to know the previous address of the same store or the store overhead from the previous year, you do not need previous dimension data in the table. With the Type 1 Dimension mapping, you can keep current data without a historical log.