So, Microsoft believes that BPEL is an interchange format. It occurred to me that they likely perceive Java as an interchange format as well. If one really, really, really wanted to... you could take C# code, convert it to Java, then convert it into VB.Net. Yes, yes - Java is an interchange format!! I don't know why that didn't occur to me earlier. And all this time I've thought of Java as a programming language.
I'm such a fool. Officially, an 'interchange format' is anything that can be used as a temporary place holder while being 'upgraded' to the Microsoft format (X/Langs, C#, etc.)
Top Ten Interchange Formats (Microsoft perspective):