EPOS

Borehole diameter is not readily available for the boreholes drilled by the ocean research drilling programmes. Available data are focused on science and drill core only. I'm sure that this information exists, probably in technical/drilling reports that are not part of the published material. In consequence, I can't fill the borehole diameter, which according to the present model does not validate as segment diameter is obligatory (which makes sense under normal circumstances).

I suggest that we make the segment diameter nilable to accommodate for the ocean research drilling data. It shouldn't break any of the existing services as xsi:nil and nilReason are optional in this case.