<status value="active"/> <date value="2014-03-26"/> <description value="A substance that is fully defined by an organic or inorganic chemical formula, includes mixtures of other chemical substances. Refine using, e.g., IUPAC codes."/> <immutable value="true"/> <compose> <include> <system value="http://terminology.hl7.org/CodeSystem/v3-EntityClass"/> <filter> <property value="concept"/> <op value="is-a"/> <value value="CHEM"/> </filter> </include> </compose> </ValueSet>