Hi,
USI/UTI are represented in FpML using the “issuer” form of partyTradeIdentifier i.e. containing issuer and tradeId elements. Interpretation as USI or UTI is (for better or worse) controlled by the choice of issuerIdScheme value:
UTI: issuerIdScheme=”http://www.fpml.org/coding-scheme/external/issuer-identifier”
USI: issuerIdScheme=”http://www.fpml.org/coding-scheme/external/cftc/issuer-identifier”
A FpML submission can contain both USI & UTI by creating an instance of partyTradeIdentifier for each, with their respective issuer elements appropriately qualified using the issuerIdScheme.