Strange... I was trying to imagine when and how this could be the case.
Data Marts are usually populated from the DW (Inmon or Data Vault), or form the DW (Kimbal model).
But is the DW populated from the source systems anyway? Why could not we populate the ODS from the source system? What about the recency of information in such ODS? Once a day? Why do we need such ODS?
This maybe due to some really strange corner case. Such could be using BI tools to create the data marts without staging tables. Then someone decided they want an ODS after all and not wanting to alter the delicate BI procedure, just did some data manipulation from the data mart to normalise the data again. You could schedule both of these processes to occur one after the other. If done often enough throughout the day .. then you have an ODS from a data mart. Certainly this is not ideal, nor would I immediately trust the quality.
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