mechanism for measurementTypes that are combinations of other measurementTypes

[mobb]

eg, ratios like slope and P-max (photosynthetic rate / irradiance), specific rates (uptake rate / biomass ), many radiometric measurements.

[mobb]

Recommendation from Jim: do not use numerator/denominator, instead suggests part_of? Or in_relation_to? For an example of a measurementType using 'has numerator', 'has denominator' see 'Ammonium Concentration' (ECSO_00001116)

Proposed:

col1	col2	col3
Mixtures	obo:part_of	carbon obo:part_of phytoplankton, nitrogen part_of water
Spatial containment
spatial-Temporal containment
Other, No physical relationship	sio:in_relation_to

[mobb]

also see issue #4