dimension vectors, expressing dimensionless-ness

[mobb]

We are using these guidelines, plus examples from existing units to assign.
https://github.com/qudt/qudt-public-repo/wiki/DimensionVector-Vocabulary-Submission-Guidelines

issues with examples. this file:
shouldn't these two quantities AngularVelocity, AngularMomentum have similar use of D?

qkdv:A0E0L0I0M0H0T-1D1
  a qudt:QuantityKindDimensionVector_CGS ;
  a qudt:QuantityKindDimensionVector_ISO ;
  a qudt:QuantityKindDimensionVector_Imperial ;
  a qudt:QuantityKindDimensionVector_SI ;
  qudt:dimensionExponentForAmountOfSubstance 0 ;
  qudt:dimensionExponentForElectricCurrent 0 ;
  qudt:dimensionExponentForLength 0 ;
  qudt:dimensionExponentForLuminousIntensity 0 ;
  qudt:dimensionExponentForMass 0 ;
  qudt:dimensionExponentForThermodynamicTemperature 0 ;
  qudt:dimensionExponentForTime -1 ;
  qudt:dimensionlessExponent 1 ;
  qudt:hasReferenceQuantityKind quantitykind:AngularVelocity ;
  qudt:latexDefinition "\\(U T^-1\\)"^^qudt:LatexString ;
  rdfs:isDefinedBy <http://qudt.org/2.1/vocab/dimensionvector> ;
  rdfs:label "A0E0L0I0M0H0T-1D1" ;
.
qkdv:A0E0L0I0M0H0T-2D0
  a qudt:QuantityKindDimensionVector_CGS ;
  a qudt:QuantityKindDimensionVector_ISO ;
  a qudt:QuantityKindDimensionVector_Imperial ;
  a qudt:QuantityKindDimensionVector_SI ;
  qudt:dimensionExponentForAmountOfSubstance 0 ;
  qudt:dimensionExponentForElectricCurrent 0 ;
  qudt:dimensionExponentForLength 0 ;
  qudt:dimensionExponentForLuminousIntensity 0 ;
  qudt:dimensionExponentForMass 0 ;
  qudt:dimensionExponentForThermodynamicTemperature 0 ;
  qudt:dimensionExponentForTime -2 ;
  qudt:dimensionlessExponent 0 ;
  qudt:hasReferenceQuantityKind quantitykind:AngularAcceleration ;
  qudt:latexDefinition "\\(U T^-2\\)"^^qudt:LatexString ;
  rdfs:isDefinedBy <http://qudt.org/2.1/vocab/dimensionvector> ;
  rdfs:label "A0E0L0I0M0H0T-2D0" ;

[steveraysteveray]

Thank you for pointing out this issue regarding dimension vectors with D1. As I look back at the vocabulary, I see 9 such vectors. My current thinking is that only one of those is valid - the one where all the other dimensions are zero. I don't recall our thinking for the other 8 cases, so I will confer with my colleagues on that.

[mobb]

thanks, Steve. We'll align our practices with your group's recommendations.

In our discussions, we were thinking that perhaps using D1 when other dimensions were not zero could be indicating that there are other dimensions which have reduced to zero - as there is no other way in the dimension vector of showing that the unit actually has them (and they are important). A fragment from one of our draft units is below, where the D1 is a stand-in for the fact that the two mass dimensions reduce to 0. Of course there is no way of knowing from this vector which dimensions were reduced, but combined with the T-1, it's a clue that they are present.

qudtUnit:MilliGM-PER-GM-HR
rdfs:label:"Milligram per Gram per Hour"@en 
qudt:conversionMultiplier: 2.7778 * 10^-7
qudt:conversionOffset: 0.0
qudt:hasDimensionVector: A0E0L0I0M0H0T-1D1
qudt:hasQuantityKind:Rate 
#probably a SpecificUptakeRate

[steveraysteveray]

Actually, we do have a mechanism to allow dimensionless quantity kinds to be distinguished, described here. So far, we are only using this mechanism for dimensionless ratios where the numerator and denominator dimensions are the same, so your example would not quite fit. In general, though, we are open to some kind of systematic approach to meet these needs. How one would slice up a given unit or quantity kind into a numerator and denominator is a wide open issue.

Incidentally, we are still resolving how to represent scientific notation for numbers (see here), but for your example, it would be 2.7778E-7 to be properly interpreted.

[mobb]

Clearly, we have not read/ingested enough yet! thanks for these specific pointers.