Thanks for your answer!
I did not know ImportMany, I have to look into it! (I'm new to MEF)
Actually I did find a nice work around.
I am not exporting ISource(s) but ISourceManager(s) which have one property, an enumeration of ISource.
Anyway, in this particular case, I don't think I can use ImportMany.
My scenario is source reprent a "data reporitoy", you got one MemoryRepository class and instance to store data in memory.
You got one FileSystemRepository class and instance to access all file as stream.
And you got one class StructureFileRepository with many instance to represent all the opened strutured file content. One instance per file. Of the same class.
How would you go about that?