A lot of extract-transform-load (ETL) work requires unloading and un-transforming first. Rather than \ETL\, it’s \L_A^{-1}T_A^{-1}ET_BL_B\. What the data provider did is \A\. What you want to do is \B\. The data provider gave you a “dump” of their data. You don’t know what it means. If you did, you could extract (subset) from it according to your needs – filter entities by some meaningful criteria and collect selected attributes.