of the latest CML schema. This one must be used for creating any new CML file. http://www.xml-cml.org/schema/cml2/core This was the first namespace used in the XML Schema definition for CML. It has been used by at least OpenBabel and the CDK , but is outdated and should no longer be used. http://www.xml-cml.org/dtd/cml1_0_1.dtd