Here is the sequence of loading a datawarehouse.

1. The source data is first loading into the staging area where data cleansing takes place.

2. The data from staging area is then loaded into dimensions/lookups.

3.Finally the Fact tables are loaded from the corresponding source tables from the staging area.

__________________ _______________ ________________
|_________________| |______________ | |_______________|
| | | | | |
|______Flat Files____| | | | |
| | Stores data | | | |
|___SQL Server Files_ | Periodically | | | |
| |------------>| Staging |--->| Target Table |
|_____Java files_____| | | Area | | |
| | | | | | |
|_____Sap Files_____| | | | | |
| | | | | | |
|___Oracle files_____ | | | | |_______________|
|_________________| | |______________| |_Data Warehouse_|
|
Different types of Relational |
Sources | ________________
| |________________|
| | |
| | |
| | ODS |
|----->| (Operational Data |
Stores Recent | Store) |
Data |________________|


The data is extracted from the different source systems.After extraction the data is transfered to the staging layer for cleansing purpose.Cleansing means LTRIM/RTRIM etc.The data is coming periodically to the staging layer.An ODS is used to store the Resent data.An ODS and the Staging Area are the two types of layer between the source system and the target system.After that the data is transformed according to the buisness needs with the help of the ETL Transformations.And then the data is finally loaded into the target system or data warehouse.