What the OSIDs call interoperability is not just the communication between two parties where we worry about the over-the-wire protocols and their associated APIs. The concern of the OSIDs is the ability to change the components of a software system. This includes the application components as well as the underlying system components.
Interoperability is the ability to swap service implementations (OSID Providers) as well as the ability to swap application components (OSID Consumers).
The goal of the OSIDs is to achieve many-to-many interoperability.
The OSID APIs are designed to be software interfaces where concerns of serialization and data store are notably absent as they are assumed to be handled under an interface as part of an OSID Provider.
From a system point of view, OSIDs appear to be high-level interfaces that leave a lot up to the imagination. From an application point of view, the OSIDs appear to be a disconnected set of low-level interfaces. The OSIDs are optimized for interoperability at the expense of the simplifying the specific needs of any particular application or development framework. The Okapia development tools close some of these gaps through many canned implementation classes based on more common programming patterns.