ISO/IEC 21823-3:2021 provides the basic concepts for IoT systems semantic interoperability, as described in the facet model of ISO/IEC 21823-1, including:

- requirements of the core ontologies for semantic interoperability;

- best practices and guidance on how to use ontologies and to develop domain-specific applications, including the need to allow for extensibility and connection to external ontologies;

- cross-domain specification and formalization of ontologies to provide harmonized utilization of existing ontologies;

- relevant IoT ontologies along with comparative study of the characteristics and approaches in terms of modularity, extensibility, reusability, scalability, interoperability with upper ontologies, and so on, and;

- use cases and service scenarios that exhibit necessities and requirements of semantic interoperability.