Re: [Gnumed-devel] Measurement conversion concepts

[Busser, Jim]

Taking two examples:

(1) first, a straight-forward measurement like

         weight

Each member of a set of weights could be passed as follows …

- let "desired" units = whatever is stored in test_type.conversion_unit

- then each test result (converted to desired units) would be

        test_result.val_num * factor

- we just need the correct factor, which must be selected from public.unit

- the conditions should require that

                        test_result.val_unit = public.unit.name_short

        AND     test_type.conversion_unit = public.basic_unit.name_short


(2) less straight forward is the case of something like

        umol/L <--> mg/dL

because the conversion will depend on the substance. Creatinine has a different 
molecular weight, and therefore a different factor, than the conversion for 
glucose or urea. It is therefore not enough to do a lookup on units alone. Some 
additional column will need to be factored in.

Does it work to let the values of such a column be null for those kinds of 
units that do not care about the substrate

        length
        weight
        time

but in the case where the substrate *does* matter, how to provide for that?

-- Jim