Wikidata:Property proposal/unit of measurement

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recommended unit of measurement[edit]

Originally proposed at Wikidata:Property proposal/Natural science

Descriptionunit in which a quantity is measured as recommended by a standard (SI, ISO, IEC, ...)
Representsunit of measurement (Q47574)
Data typeItem
Domainsubclasses of individual quantity (Q71550118) or its subclasses
Allowed valuesinstances of SI or accepted non-SI unit (Q87252761) or its subclasses
Example 1mass (Q11423) → kilogram (Q11570)
Example 2area (Q11500) → square metre (Q25343)
Example 3speed (Q3711325) → metre per second (Q182429), kilometre per hour (Q180154)
Example 4magnetic moment (Q242657) → ampere square metre (Q71581529)
SourceISO/IEC 80000 (Q568496)
Planned usemove unit-valued statements from measurement scale (P1880) to this new property; enter all values listed in ISO/IEC 80000 (Q568496); check consistency with the Wolfram Language (Q15241057) quantity and unit ontology (using the function QuantityVariableCanonicalUnit[...] and CompatibleUnitQ[...])
Number of IDs in sourcehundreds
Expected completenessalways incomplete (Q21873886)
See alsomeasured physical quantity (P111) (inverse of this new property), measures (P2575) (from measurement device to quantity), measurement scale (P1880) (from phenomenon to scale)

Motivation[edit]

The property measurement scale (P1880) is currently used in some hybrid way: It links a) a phenomenon (earthquake) to a scale (Richter scale) and b) a quantity (length) to a unit (metre). I find those uses are disjoint and could better be handled by two properties, each with their separate set of constraints (P1880 accepts as values "scales", and the proposed property "units").

Summary of the history of the existing measurement scale (P1880) (as I understand it): In the proposal discussion the description mentions units, but the examples are all of type a). Later the property was used mostly for type a), with a few uses of b). Some month ago I started working intensively on improving the quantity and unit ontology in Wikidata, and - lacking an alternative - continued entering units for quantities (use b)). I now feel that this mix-up of concepts will make the use, maintenance, choice of label and description, and consistency checks more difficult.

Therefore I propose this new property. Toni 001 (talk) 14:51, 22 December 2019 (UTC)[reply]

There is precedent for modeling quantities and units by making a connection from the quantity to the unit (not all provide the other direction). For instance:

Toni 001 (talk) 09:26, 8 January 2020 (UTC)[reply]

Discussion[edit]

 Comment If this is a strict inverse of the existing property then it's really not needed I think. ArthurPSmith (talk) 19:31, 23 December 2019 (UTC)[reply]
In principle measured physical quantity (P111) should be enough to state all quantity-unit connections. However, ISO 80000-1:2009 Quantities and units—Part 1: General (Q26711930) emphasizes that "quantities come first and units then follow". If we want to follow this interpretation then it seems natural to have unit statements on the quantity items. But then there is also a more practical issue to consider: There might be tens or hundreds of quantities that are measured in, say, metre (Q11573): With the currently available P111 the metre items will become very crowded. This is somewhat analogous to listing all cities on the country items. The problem is probably the worst for 1 (Q199) (the "dimensionless unit"). Toni 001 (talk) 12:51, 24 December 2019 (UTC)[reply]
 Oppose per Arthur (I fear a lot of bloat coming from this). Mahir256 (talk) 20:02, 23 December 2019 (UTC)[reply]
@Mahir256: Arthur raised some valid concern, so I gave some additional motivation why this property is useful and better suited than measured physical quantity (P111). Note that this is not simply creating additional data, but would be a better location for data already in measurement scale (P1880). For instance, now we can't (easily or cleanly) add property constraints that would tell an editor "hey, that's not a unit". And I've been reluctant to use P111 as that would mean adding countless statements of the form 1 (Q199)measured physical quantity (P111)static friction factor, 1 (Q199)measured physical quantity (P111)dynamic friction factor, 1 (Q199)measured physical quantity (P111)mass ratio, 1 (Q199)measured physical quantity (P111)linear expansion coefficient, 1 (Q199)measured physical quantity (P111)cubic expansion coefficient, 1 (Q199)measured physical quantity (P111)level of field quantity, ... to 1 (Q199) Toni 001 (talk) 10:09, 26 December 2019 (UTC)[reply]
 Comment How about
pattern
quantityhas dimensiondimension
dimensionunit of measurementunitsystem of unitssystem of units

example
speed (Q3711325)has dimensionlength per time
length per timeunit of measurementcentimetre per second (Q18413919)system of unitscentimeter–gram–second system of units (Q26240)
example
coefficient of friction (Q1932524)has dimensiondimension 1
dimension 1unit of measurementdimensionless unit (Q1618549)

? This might help reduce bloat since there are fewer quantity–dimension associations and dimension–unit associations than there are quantity–unit associations.
And where there’s no concept of dimension, maybe
pattern
phenomenon“quantified on [scale]” (measurement scale (P1880))scale

? (@Toni 001: It seems that maybe the vague label “measured by” was what invited in the first place the questionable ‘use b)‘ of measurement scale (P1880) which this proposal is now supposed to sort out. So a clearer might help also.)
―BlaueBlüte (talk) 07:46, 8 January 2020 (UTC)[reply]
@BlaueBlüte: About your second point first: Yes, both label and description are (or were) vague, and looking at the property proposal discussion did not help because unit is mentioned there. Sometimes I have seen confusion about what the difference is between a unit and a scale, and this might have contributed to the confusing use of the property (P1880). Quick explanation: Temperature is measured by a temperature scale (say, Celsius scale, Kelvin scale, ...) and measure in the unit degree Celsius, Kelvin, ...; the scale is used to define the unit.
Now about your first point: torque (Q48103) and energy (Q11379) have the same ISQ dimension (P4020), yet their values are expressed in different units: newton metre (Q215571) and joule (Q25269), respectively (note that this is in the same unit and quantity system). Therefore the unit needs to be attached to the quantity. Toni 001 (talk) 08:14, 8 January 2020 (UTC)[reply]
@Toni 001: Good point about newton metre (Q215571) vs. joule (Q25269).
I just saw that there’s also unit of torque (Q21813488) and unit of energy (Q2916980)—and unit of length (Q1978718), since you brought up metre (Q11573) above. Can we fit those into this in any helpful way? E.g.,
pattern
quantityclass of units of measurementunit of quantity
unitinstance of (P31)unit of quantity
Then we’d have rather than (speaking of crowding)
example
length (Q36253)unit of measurementmetre (Q11573)
length (Q36253)unit of measurementyard (Q482798)
length (Q36253)unit of measurementfoot (Q3710)
width (Q35059)unit of measurementmetre (Q11573)
width (Q35059)unit of measurementyard (Q482798)
width (Q35059)unit of measurementfoot (Q3710)
depth (Q3250078)unit of measurementmetre (Q11573)
depth (Q3250078)unit of measurementyard (Q482798)
depth (Q3250078)unit of measurementfoot (Q3710)
depth (Q930412)unit of measurementmetre (Q11573)
depth (Q930412)unit of measurementyard (Q482798)
depth (Q930412)unit of measurementfoot (Q3710)

As for “measured by”, the more specific preposition on might help clarify the semantics of measurement scale (P1880) and be sufficiently common, cf. some usage statistics.
―BlaueBlüte (talk) 09:22, 8 January 2020 (UTC)[reply]
@BlaueBlüte: A general remark: Classes like unit of length (Q1978718) are (very closely related to) what is called kind of quantity, a concept which is explained nicely in Defining 'kind of quantity' (Q71548419). The idea is that length, radius, wavelength, ... are all kind of length and lengths are measured in metre, millimetre, inch, .... This is already modeled to some extend, for instance by statements like radius (Q173817)subclass of (P279)length (Q36253) and metre (Q11573)measured physical quantity (P111)length (Q36253). Though this has not been stated anywhere formally, yet (to my knowledge). Considering length (Q36253) as both a quantity and a kind of quantity makes classes like unit of length (Q1978718) unnecessary. Tackling kind of quantity is on my to do / wish list: By proposing one or more models (either with or without new properties) and forming consensus.
Now to this property: You bring up a good point about unit of measurement-statements becoming crowded. The way out is to not list all possible units, but only typically used units or units given in references. So, while length - by being a very general term - might have quite a few statements, atomic mass (Q3840065) might only list kilogram and dalton.
I have updated the motivation with a (non-exhaustive) list of well-known ontologies that model the quantity-unit relation in the same way as proposed here. Toni 001 (talk) 10:16, 8 January 2020 (UTC)[reply]
  •  Comment @Toni 001, BlaueBlüte: I think I would support this if it was limited to only SI units. We have conversion to SI unit (P2370) now; maybe the label here could be "SI unit of measurement" to correspond? ArthurPSmith (talk) 18:12, 6 March 2020 (UTC)[reply]
    • @ArthurPSmith: That is actually the use case that I have in mind. I'd like to enter and add sources for the unit of measurement given in standards like the SI Brochure (Q69526309) and ISO/IEC 80000 (Q568496). There are certain units that are "accepted for use with the SI", like minute and hour, which I'd like to include, too, because there are officially accepted (page 145 of SI Brochure (9th edition) (Q68977219)). Apart from that, the ISO/IEC standards list a few additional units for their conversion factors (as annex). We could include those, too, but with deprecated rank because they are not recommended any more. So, in summary I agree with the purpose of this property. Toni 001 (talk) 08:15, 7 March 2020 (UTC)[reply]
      • @ArthurPSmith: I restricted the allowed values to SI or SI-accepted units. Toni 001 (talk) 06:08, 10 March 2020 (UTC)[reply]
        • @Toni 001: That still seems too general to me. I'd prefer limiting it to just coherent SI unit (Q69197847) so there's basically one allowed value in most cases. ArthurPSmith (talk) 12:34, 10 March 2020 (UTC)[reply]
          • @ArthurPSmith: I'm open to restricting this to coherent SI units (thereby making the value unique - modulo naming variants like N vs kg m/s^2 or C vs A s). But first, let's consider this: ISO/IEC 80000 lists in some cases a non-coherent SI unit. For instance, the unit of spectral radiant flux (Q81062859) is given as watt per nanometre (Q81062869). Of course, that does not prevent one to specify the same quantity in a different (SI) unit. However, it indicates which unit is typical for the typical size of a quantity. I think there is a certain value in preserving this information. Allowing those non-coherent SI units (and requiring a source to limit proliferation) will still allow tools to "normalize" quantities by converting to units in the class coherent SI unit (Q69197847). (One more question: If the standard reads W/nm and we enter W/m, can we still quote the source? I mean, technically this is [nearly] the same, but well, I'm a little uneasy. What do you think?) Thanks. Toni 001 (talk) 07:47, 11 March 2020 (UTC)[reply]
            • @Toni 001: I'm not sure I follow. You can use whatever unit you like when you enter a quantity value, so in general yes you should follow the units that the source provides. Or perhaps you're just arguing that "coherent SI units" isn't the right restriction here. Is ISO/IEC 80000 a better way (I'm not familiar with it though)? ArthurPSmith (talk) 12:58, 11 March 2020 (UTC)[reply]
              • @ArthurPSmith: I'm referring to allowed values of the property proposed here. Quick background: The ISQ (International System of Quantities) is to quantities what the SI is to units. ISO and IEC have standardized in the 80000 series on the order of 1000 quantities of the ISQ. The definitions, symbols, (official) names and units listed in those standards are used more or less consistently across the literature in different areas of science (and in Wikipedia, too). It is those ~1000 quantities that I'd like to polish in Wikidata first (which I guess I'll need till the end of this year at my current rate of about 1 to 2 quantities per day). Those standards (14 parts from different areas of science as diverse as mechanics, thermodynamics, light and radiation, electromagnetism, acoustics, information science, ...) are tables listing per row the name, symbol, definition and unit of a quantity. Now to my point: This unit is not always coherent as sometimes for instance nm is stated instead of the coherent m. Apart from that, some units are not part of the SI (yet), for instance information units like the bit. In summary, we are talking about 1000 values for this property - not too much (in my opinion) to manage manually and requiring coherent SI units might be a little too strict. Toni 001 (talk) 08:58, 12 March 2020 (UTC)[reply]



Tobias1984
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Physikerwelt
Pamputt
Petermahlzahn
Jibe-b
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Daniel Mietchen
TomT0m
ArthurPSmith
Mu301
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Toni 001
Marc André Miron
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CarlFriedberg
Crocodilecoup
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Amorenobr (talk) 01:27, 3 August 2022 (UTC)[reply]
Valverde667 (talk) 16:07, 4 August 2022 (UTC)[reply]
fgnievinski

Notified participants of WikiProject Physics I'm ready to create this property, I think Toni 001 has adequately addressed all the existing concerns and made good a good case for why it is needed. However, I'd like to make sure it's first brought to the attention of other interested parties to give a chance to raise any concerns they might have before creation occurs. If anyone thinks of other relevant WikiProjects ping them here please. If no further concerns are raised then I'll create this one on Friday. --SilentSpike (talk) 14:02, 6 April 2020 (UTC)[reply]

@Toni 001, BlaueBlüte, ChristianKl, ArthurPSmith: ✓ Done at recommended unit of measurement (P8111). Toni would you be so kind as to add the appropriate "stated in" references to the property examples (as I don't have full access to the standards) to show future editors how that's done? --SilentSpike (talk) 10:42, 10 April 2020 (UTC)[reply]

@SilentSpike: Thanks for the creation. And thanks to everybody who participated in this discussion. I'll work on polishing this property and start adding values with sources. Toni 001 (talk) 10:48, 10 April 2020 (UTC)[reply]
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