Jean-Claude, I think you've hit the nail on the head. That has really crystallised something for me. The point is that we can't actually define the boundaries of the experiment until after it is done. We don't know where it stops so applying a data model in advance is very challenging (although not impossible as long as it is sufficiently extendable).

I think this maps onto what I wrote last night. I imagine a 'LabStream' which the experimentalist then structures into a description of the 'experiment' after they've decided how to frame it.