Certainly a through Impact and risk assessment is absolutely necessary and Always recommended. Else Data warehouse will have unrelated data sets. The relationships will get broken .Any historical data will get orphaned or corrupted depending on the design. There is a good possibility for duplicates. This can make bring a lot is issues and make the ware house unstable or unusable as the data might not be comparable to the source.
data level security if any can get broken.
if the switch to a new data source is going to happen, any historical data will have to start afresh.
You might typically want to do a Initial Full load and then followed by Incremental load. Archive any old data. its like starting afresh (Truncate - full load).
The issue list can be way longer,
Impact and risk analysis and mitigation plan is absolutely necessary.
Thanks for the information,
Everynight we are updating the DW from CDC via ETL. What kind of changes from your ERP system do you need to know from the BA's that will impact your DW?
What I can think of are any ERP Table Changes (Add, remove) and field changes (add, remove, changing the definition (meaning) of a field)
Whoever is in charge of the BI team needs to have an agreement with whoever is in charge of the BA's, to make the BI team aware of any proposed/pending changes as soon as possible, and appropriate notification procedures should be put in place.
At first notification of proposed changes, BI team should provide a fast, high level impact analysis on how changes will affect BI, and time estimate required for BI to be updated.
At this point, it depends on the severity of the changes, and it is usually all relative.If BA's are making minor changes to the ERP, it will not take them very long, and it will not take BI team very long to account for those minor changes. On the other hand, if the BA's are making extensive changes to the ERP, it will take them more time for changes, as well as testing, so it gives BI team more time to make changes as well.
The key is communication of those changes when they are proposed, not when they are being made. Management, along with everyone else affected, needs to be aware of all facets of the changes in order to determine the proper solution.