Extracting and loading data from operational systems to a data warehouse varies in complexity. The process can be simple if there is a direct correlation between the source data and the data that should appear in the data warehouse: for example, if all the source data from a single operational system is in the correct format, and does not have to be modified in any way. The process can also be complex: for example, if source data resides in multiple, heterogeneous operational systems, and requires significant formatting and modification before loading.
The extraction and load process involves: