Understanding dimension history types
By default, dimension tables are defined as history type 2, meaning that a new record is added each time a record is updated (as opposed to updating the same record). In the data warehouse, dimension tables always contain an object identifier column which is the table name appended with "_OID". However, when a dimension table’s history type is 2, an additional "version" column is added as the dimension table’s Primary Key. This column, which is used to identify the version, has the same name as the table, but is appended with "VID".
The flowing figure shows the Customer_VID and Customer_OID (object identifier) columns in the Customers dimension table:
If a dimension table is defined as history type 1 and one or more of the columns in the corresponding data warehouse are defined as type 2, records in the dimension table will simply be replaced with the most up-to-date record in the corresponding data warehouse table.