Every valid ISIN request submitted to the DSB will be returned with the CFI code as part of the ISIN record. The CFI code is constructed from 6 attributes that are either explicitly submitted by the user (in cases where there are multiple choices for a specific instrument) or derived by the DSB (in cases where there is a clear and accurate interpretation for a specific instrument).
The asset class based CFI taxonomy is outlined in each of the Product Definition documents published here