Unification of medical coding systems is a perceived need involving a long-term task. Standards will support convergence of present coding systems towards a coherent set of tools. The Project Team "Model for Representation of Semantics" (CEN/TC251/PT003-MOSE) modeled existing tools to obtain a vocabulary apt to describe coding systems and terminologies. Requirements on faithfulness and safety, usefulness and purposiveness, coherence and integration were worked out, and the MOSE's 10 key principles for Standards in Medical Semantics were established.