Thirty years ago, interoperability was a lot simpler. If you could exchange data between two IT systems, you had interoperability. In the three decades since, the amount of data and the number of sources of data for an individual or a population have both increased exponentially.
Now interoperability is about accessing data across many systems, both inside and outside the organisation, as a single, concordant view, and presenting it to clinicians in a way that is usable and actionable in their workflows.