OneM2M standard is a global initiative led jointly by major standardization organizations around the world in order to come up with a unique standard for M2M communications. Prior standards, but also oneM2M, while focusing on achieving interoperability at the communication level, fail or lack to achieve full interoperability at the semantic data level. An expressive ontology for IoT called IoT-O has been defined making best use of already defined ontologies in specific domains such as sensor, observation, service, quantity kind, units, or time. IoT-O defines also some missing concepts relevant for IoT such as thing, actuator, actuation, or manager. The extension of the oneM2M standard to support semantic data interoperability based on IoT-O is discussed. Finally, through comprehensive real use cases, benefits of the augmented standard are demonstrated ranging from heterogeneous devices interoperability to autonomic behavior achieved by automated reasoning.