I assume when you say "there is a precise definition, so I won't give a link" you mean that you've already given the precise definition in italics above (otherwise you are providing poor interoperability yourself by hiding the definition).I think that was true in the 90s. But you probably are not aware of developments in MS the last few years. You might be surprised.That's not what "open" means although having unrestricted access to the code certainly means the interfaces are completely understood (unlike proprietary software).How many open source projects are 'open' in the sense of being interoperable with other software systems? Coming up with a conforming common standard is a non-starter IMO.
They tend to be 'silos of automation'.
Interoperability is a characteristic of a product or system, whose interfaces are completely understood, to work with other products or systems, at present or future, in either implementation or access, without any restrictions.
e.g. Quantlib, Boost etc.?
It would seem that Microsoft is a far worse silo with far less interoperability than most open source projects.
Personally, I have no interest in smart phone interop, so no need starting a brush fire,
Back to topic: how many open-source codes are interoperable? (btw there is a precise definition, so I won't give a link)?
In any case, I assume we need to construct an (M+N)x(M+N) matrix of the M proprietary & N open-source code in the world and test if software i interoperates with software j. Of course, if i doesn't interoperate with j, then there's the question of who's to blame.
That definition also alludes to "the future" as an element of interoperability. Are the file formats of Microsoft products open and controlled by an independent body or are they closed and subject to the whim's of Microsoft product development? Maybe that's something that's changed since the 90s?