Depends. Things are rarely in absolutes :) If you serialise / deserialise you are probably coupled to an underlying type. Modify it instead of extending it and

Depends. Things are rarely in absolutes :) If you serialise / deserialise you are probably coupled to an underlying type. Modify it instead of extending it and you have pain. If you parse the raw message, or serialise into a hash, or dynamic type then you have one place to make amends (your parser). Taking things further you can version your messages and map them to versions of parsers, as such you'd never violate OCP (or at least simply mitigate). Granted all of which is additional complexity compared to your stereotypical ball of mud / monolith that'll let you refactor field name changes etc to your hearts content. Obviously ball of mud approach has draw backs too...