The DFDL language took into account the capability of WMB MRM and WTX type trees during its design. OGF DFDL should be able to model everything that MRM can model, though not always in exactly the same way. IBM DFDL 1.0 does not yet implement the full DFDL spec so there are some things right now that MRM can do that IBM DFDL can't (eg, unordered data). Until IBM DFDL is complete, it may be necessary to use MRM in such scenarios.