Here is Admiral Edmund P. Giambastiani Jr, Commander of the US Joint Forces Command, talking to the US Congress in March 2003 (html, pdf). He talks a great deal about collaborative partnerships, coalition partners and "jointness". Here is the key paragraph:
Coherent jointness is the third characteristic of future joint operations, which facilitates coordinated, synergistic employment of the full range of joint capabilities to achieve the desired affects. The interoperability of joint and Service capabilities further enables, and amplifies this common joint ethos. To achieve this synergy of doctrinal, organizational, and human factors, future capabilities must be “born joint.” Interoperability by design in the first instance will permit true integration. It will solve, by moving beyond, the current challenge of de-conflicting service systems that do not talk to each other. Born joint capabilities will require a greater depth of understanding of joint capabilities, an agreed Joint Operating Concept and a shared joint warfighting culture. It enables the execution of seamlessly joint actions at levels appropriate to the mission.
According to Gates, interoperability comes from XML. (The official Microsoft line is that interoperability is all about different software products working together.)
According to Giambastiani, interoperability comes from jointness. (This is clearly system interoperability rather than just software interoperability.) I see this as establishing a significant mandate for collaborative composition.