An empty unit string positively indicates that the corresponding quantity is dimensionless.
Since an empty string does not conform to the grammars below,
this also must be checked for before unit-parsing starts.
However an empty string might also naturally appear when units information is simply missing, so that this in an insecure way of ‘positively indicating’ that a quantity is dimensionless.
Proposal: change the ‘positively indicating’ string to be "1" for the VOUnits syntax, and adjust the VOUnits grammar to make this a legal units string.
This was discussed on the semantics@ivoa.net list, in 2021 December, with a rough consensus in favour of this change, and implementing it (Norman) in the Unity library doesn't throw up any major problems (but see issue #8). So if the consensus survives, this change should appear in the VOUnits document for 1.1
nxg
commented
2 years ago
In VOUnits 1.0, there is text:
However an empty string might also naturally appear when units information is simply missing, so that this in an insecure way of ‘positively indicating’ that a quantity is dimensionless.
Proposal: change the ‘positively indicating’ string to be
"1"for the VOUnits syntax, and adjust the VOUnits grammar to make this a legal units string.This was discussed on the semantics@ivoa.net list, in 2021 December, with a rough consensus in favour of this change, and implementing it (Norman) in the Unity library doesn't throw up any major problems (but see issue #8). So if the consensus survives, this change should appear in the VOUnits document for 1.1