Fix and Extend Sustainability Quantities and Units

[jmkeil]

This PR addresses #87. The initial PR is thought as a baseline for discussion and further collaborative changes.

[HajoRijgersberg]

Thanx again so much, Jan Martin! In general it really looks very good.

I only have some more detailed questions, though important. I'll process them in the order that I read them from your proposed changes and your comments:

• You indicate: 'om:carbonDioxideEquivalent (I think) needs to be defined based as (W m⁻² yr kg⁻¹) / (W m⁻² yr kg⁻¹).' I'm not sure what om:carbonDioxideEquivalent is now, please help me (it's just due to not grasping something from my side). Is it a quantity or a unit?
• From your subsequent comment I understand that CO2-eq (the symbol for the above-mentioned concept?) is a unit. My first presumption is that we should have units like gCO2eq (with or without dash, that is not specifically my point now), i.e., with g, t, kg, etc.. Second, I feel we would have to go for your second option, creating one ambiguous unit, as done e.g. with ppm, as apparently that is what the domain/field wants or is used to, and is open for future improvement. I guess you know the work of Marcus Foster, important work in that area; there is really a lot to improve, starting with e.g. mass ratio units, mol, etc. But, that would be something for an international conference about units, that we should subsequently follow. But any point that Marcus or we could make can be quite important, I think, depending on whether ir would be picked up, or when. Indeed I see you gave option 1 a try. Understandable. But not sure at this moment... (How) does this also relate to definitions such as om:CarbonDioxideEquivalentGWPMass? Is that also a part of option 1 or should I regard that differently (just for my understanding again).

Looking forward to your response; thanx in advance, and appreciate all your work so much!

Best, Hajo

[jmkeil]

Thanks for the comment.

Coming back after months to this, I had some time to think about this and came up with this conclusion:

Most open questions and confusions go back to the question whether we want to model it in the "Realists" way or the "Systematists" way, as noted in The next 50 years of the SI: a review of the opportunities for the e-Science age:

De Boer [14] identifies two schools of thought, the Realists (in which units are regarded as real physical entities) and Systematists (in which the symbols for quantities, dimensions and units represent abstract mathematical concepts which may be manipulated algebraically). The latter view has prevailed, […]

Variant 1. was to the "Realists" way by expressing the origin of quantities in the units. Variant 2. was closer to the "Systematists" way, but stopped halfway through. To fully apply the "Systematists" way, we would not need units like "kg CO2eq" or "CO2eq" at all, but just use om:one or "kg".

I think, OM is closer to the "Systematists" way, as e.g. there is only one "ppm" and not multiple "ppm"s like for volume ("ppmv") and for mass ("ppmw" [sic!]). Because of that, I will continue in that direction and remove the CO2eq specific units again. But we could add these special names as alternative labels or symbols.

[jmkeil]

I just pushed the changes to adhere in this issue to the systematists view.

@HajoRijgersberg Please have a look whether this fits to the OM standards.

Known open tasks are to add dimension and classes of units to some of the new quantity kinds.

[jmkeil]

The latest push

• adds all missing dimensions and unit classes to sustainability quantities,
• merges om:CarbonDioxideEquivalentGwp100 and om:GlobalWarmingPotential100YearHorizon (fixing an duplication error I introduced last week), and
• improves sustainability quantities descriptions.

So, given it satisfies your (@HajoRijgersberg) expectations on the structure, I think the PR is ready to merge.