The nomenclature of interoperability is growing and confusing. The openEHR specifications aim to provide a robust basis for sematic interoperability: when machines as well as people can process the information. Here, to help with the issues around interoperability is a post on the list from Ian McNicoll:
The initial argument really hinges on whether the most minimum
communication of an email with attached clinical pdf, by being human
interpretible meets the definition of 'functional interoperabillity'.
...